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91-658: Echo Mountain is a mountain promontory of the San Gabriel Mountains , in the Angeles National Forest above Altadena , in Los Angeles County, California . Echo Mountain was shaped from an alluvial fan between Rubio and Las Flores canyons. It is geographically defined by Castle Canyon to its leeward side, Rubio Canyon at its foot, and Las Flores Canyon on its windward side. Echo has a mean elevation of 3,207 feet (977 m). It

182-658: A mountain range located in northern Los Angeles County and western San Bernardino County, California , United States. The mountain range is part of the Transverse Ranges and lies between the Los Angeles Basin and the Mojave Desert , with Interstate 5 to the west and Interstate 15 to the east. The range lies in, and is surrounded by, the Angeles and San Bernardino National Forests, with

273-511: A $ 45 million project to reconstruct the roadway, construct soldier pile retaining walls, repair drainage systems, install rockfall protection, and provide asphalt concrete overlay and traffic striping, should begin in fall 2010." In 2011, the planned repair of the road was abruptly terminated, due to concern of high future maintenance costs, and potential impact on the local bighorn sheep population. However, in October 2016, Caltrans announced it

364-542: A broader aridification trend. The EMCI ended 18 million years ago, giving way to the Middle Miocene Warm Interval (MMWI), the warmest part of which was the MMCO that began 16 million years ago. As the world transitioned into the MMCO, carbon dioxide concentrations varied between 300 and 500 ppm. Global annual mean surface temperature during the MMCO was about 18.4 °C. MMCO warmth was driven by

455-529: A clade of large terrestrial predatory crocodyliformes distantly related to modern crocodilians, from which they likely diverged over 180 million years ago, are known from the Miocene of South America. The last Desmostylians thrived during this period before becoming the only extinct marine mammal order. The pinnipeds , which appeared near the end of the Oligocene, became more aquatic. A prominent genus

546-570: A cooler, drier climate. C 4 grasses, which are able to assimilate carbon dioxide and water more efficiently than C 3 grasses, expanded to become ecologically significant near the end of the Miocene between 6 and 7 million years ago, although they did not expand northward during the Late Miocene. The expansion of grasslands and radiations among terrestrial herbivores correlates to fluctuations in CO 2 . One study, however, has attributed

637-486: A good analogue for future warmer climates caused by anthropogenic global warming , with this being especially true of the global climate during the Middle Miocene Climatic Optimum (MMCO), because the last time carbon dioxide levels were comparable to projected future atmospheric carbon dioxide levels resulting from anthropogenic climate change was during the MMCO. The Ross Sea margin of

728-435: A good model for a "living fossil". Eucalyptus fossil leaves occur in the Miocene of New Zealand , where the genus is not native today, but have been introduced from Australia . Both marine and continental fauna were fairly modern, although marine mammals were less numerous. Only in isolated South America and Australia did widely divergent fauna exist. In Eurasia, genus richness shifted southward to lower latitudes from

819-502: A hiker gets lost or stuck on a mountain ledge or may fall downhill. Some of the more extreme cases of emergency search-and-rescue efforts will often be given air time on Los Angeles television and radio newscasts. The Pacific Crest Trail passes along the mountain ridge. During the winter, many Southern California mountaineers climb a variety of snow routes and even some ice routes in the San Gabriel Mountains. Baldy Bowl

910-668: A large fault block between the San Andreas Fault Zone to the north, and the San Gabriel Fault and the Sierra Madre and Cucamonga Fault Zones to the south. This tectonic block was uplifted during the Miocene and has since been dissected by numerous rivers and washes. The highest elevation, Mount San Antonio (Mount Baldy) at 10,069 feet (3,069 m), rises towards the eastern extremity of

1001-598: A major expansion of Antarctic glaciers. This severed the connection between the Indian Ocean and the Mediterranean Sea and formed the present land connection between Afro-Arabia and Eurasia. The subsequent uplift of mountains in the western Mediterranean region and a global fall in sea levels combined to cause a temporary drying up of the Mediterranean Sea (known as the Messinian salinity crisis ) near

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1092-480: A major expansion of grass-grazer ecosystems . Herds of large, swift grazers were hunted by predators across broad sweeps of open grasslands , displacing desert, woodland, and browsers . The higher organic content and water retention of the deeper and richer grassland soils , with long-term burial of carbon in sediments, produced a carbon and water vapor sink. This, combined with higher surface albedo and lower evapotranspiration of grassland, contributed to

1183-657: A nearly two-hour trip. Reopening Highway 39 would cut the drive-time to the Waterman Ski Area in half and shorten the trip east to Wrightwood. According to the Caltrans District Seven "Inside Seven" Newsletter, "Two projects that will address those issues and get the highway reopened are scheduled for construction soon. The first, building two retaining walls near the city of Azusa from Old San Gabriel Canyon Road to approximately 4 miles (6.4 km) south of SR-2, could begin in mid-2009. The second,

1274-602: A significant drop in atmospheric carbon dioxide levels. Both continental and oceanic thermal gradients in mid-latitudes during the Early Miocene were very similar to those in the present. Global cooling caused the East Asian Summer Monsoon (EASM) to begin to take on its modern form during the Early Miocene. From 22.1 to 19.7 Ma, the Xining Basin experienced relative warmth and humidity amidst

1365-700: A significant local decline along the northeastern coast of Australia during the Tortonian, most likely due to warming seawater. Cetaceans attained their greatest diversity during the Miocene, with over 20 recognized genera of baleen whales in comparison to only six living genera. This diversification correlates with emergence of gigantic macro-predators such as megatoothed sharks and raptorial sperm whales . Prominent examples are O. megalodon and L. melvillei . Other notable large sharks were O. chubutensis , Isurus hastalis , and Hemipristis serra . Crocodilians also showed signs of diversification during

1456-627: A steep, rugged and precipitous gorge. The two meet at San Gabriel Reservoir , and turn south, boring through the southern portion of the San Gabriels, emptying of the mountains near Azusa into the urban San Gabriel Valley , and eventually to the Pacific Ocean near Seal Beach . San Gabriel Mountains peaks within the Angeles National Forest include: The climate of the range varies with elevation from continental to

1547-651: A zone of low rainfall in the Late Miocene. The Indian Plate continued to collide with the Eurasian Plate , creating new mountain ranges and uplifting the Tibetan Plateau , resulting in the rain shadowing and aridification of the Asian interior. The Tian Shan experienced significant uplift in the Late Miocene, blocking westerlies from coming into the Tarim Basin and drying it as a result. At

1638-542: Is by far the most popular route, getting hundreds of climbers per season. There are many other routes, offering a variety of choices. Rock climbing is not as common in the San Gabriel Range as it is in neighboring areas, as this range is famous for loose rock. Various faults crisscross the range, making it one of the steepest and fastest-growing ranges in the world. Plate tectonic activity breaks up most rock, making it unsuitable for rock climbing. Williamson Rock

1729-495: Is most visible as a short mountain extension whose ridge protrudes below the peak of Inspiration Point. Echo Mountain's name is derived from the number of repetitions one's voice could emit into Castle Canyon. Boy Scout projects were made to find the "sweet spot" where the largest number of repetitions could be heard. During the days of the Mount Lowe Railway "echophones" were set up to assist in voice projections near

1820-622: Is much better, and it is open much of the winter. State Route 39 connected the city of Azusa with the Angeles Crest Highway until it was seriously damaged by landslides, first in 1978, and again in 2005. The highway was opened to emergency crews in February 2003. People heading to Mount Waterman must now travel west to Pasadena and then travel on the Angeles Crest Highway (Highway 2) in La Cañada Flintridge,

1911-682: Is of particular interest to geologists and palaeoclimatologists because major phases of the geology of the Himalaya occurred during that epoch, affecting monsoonal patterns in Asia, which were interlinked with glacial periods in the northern hemisphere. The Miocene faunal stages from youngest to oldest are typically named according to the International Commission on Stratigraphy : Regionally, other systems are used, based on characteristic land mammals; some of them overlap with

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2002-559: The Middle Miocene Climate Transition (MMCT). Abrupt increases in opal deposition indicate this cooling was driven by enhanced drawdown of carbon dioxide via silicate weathering. The MMCT caused a sea surface temperature (SST) drop of approximately 6 °C in the North Atlantic. The drop in benthic foraminiferal δ O values was most noticeable in the waters around Antarctica, suggesting cooling

2093-543: The San Andreas Fault as its northern border. The highest peak in the range is Mount San Antonio , commonly referred to as Mt. Baldy. Mount Wilson is another notable peak, known for the Mount Wilson Observatory and the antenna farm that houses many of the transmitters for local media. The observatory may be visited by the public. On October 10, 2014, Barack Obama designated the area

2184-526: The San Gabriel Mountains National Monument . The Trust for Public Land has protected more than 3,800 acres (1,500 ha) of land in the San Gabriel Mountains, its foothills, and the Angeles National Forest. Much of the range features rolling peaks. The range lacks craggy features, but contains a large number of canyons and is generally very rugged and difficult to traverse. The San Gabriel Mountains are composed of

2275-651: The Victor Valley and the western Cajon Valley. Past its junction with Angeles Forest Highway, traveling east, Angeles Crest Highway features blind curves, various bumps, and potholes. This section of the "Crest" is closed during the winter due to rockfall and avalanche hazards. State Route 2, just past Mountain High , is called the Big Pines Highway to the Route 138 junction. Another key county route through,

2366-560: The carbon cycle occurred approximately 6 Ma, causing continental carbon reservoirs to no longer expand during cold spells, as they had done during cold periods in the Oligocene and most of the Miocene. At the end of the Miocene, global temperatures rose again as the amplitude of Earth's obliquity increased, which caused increased aridity in Central Asia. Around 5.5 Ma, the EAWM underwent a period of rapid intensification. Life during

2457-710: The Central Paratethys, cut off from sources of freshwater input by its separation from the Eastern Paratethys. From 13.36 to 12.65 Ma, the Central Paratethys was characterised by open marine conditions, before the reopening of the Bârlad Strait resulted in a shift to brackish-marine conditions in the Central Paratethys, causing the Badenian-Sarmatian Extinction Event. As a result of the Bârlad Strait's reopening,

2548-837: The Early to the Middle Miocene. Europe's large mammal diversity significantly declined during the Late Miocene. In the Early Miocene, several Oligocene groups were still diverse, including nimravids , entelodonts , and three-toed equids. As in the previous Oligocene Epoch, oreodonts were still diverse, only to disappear in the earliest Pliocene. During the later Miocene mammals were more modern, with easily recognizable canids , bears , red pandas , procyonids , equids , beavers , deer , camelids , and whales , along with now-extinct groups like borophagine canids , certain gomphotheres , three-toed horses , and hornless rhinos like Teleoceras and Aphelos . The late Miocene also marks

2639-720: The East Antarctic Ice Sheet (EAIS) was highly dynamic during the Early Miocene. The Miocene began with the Early Miocene Cool Event (Mi-1) around 23 million years ago, which marked the start of the Early Miocene Cool Interval (EMCI). This cool event occurred immediately after the Oligocene-Miocene Transition (OMT) during a major expansion of Antarctica's ice sheets, but was not associated with

2730-601: The East Asian Winter Monsoon (EAWM) became stronger synchronously with a southward shift of the subarctic front. Greenland may have begun to have large glaciers as early as 8 to 7 Ma, although the climate for the most part remained warm enough to support forests there well into the Pliocene. Zhejiang, China was noticeably more humid than today. In the Great Rift Valley of Kenya , there

2821-460: The LMC; extratropical sea surface temperatures dropped substantially by approximately 7–9 °C. 41 kyr obliquity cycles became the dominant orbital climatic control 7.7 Ma and this dominance strengthened 6.4 Ma. Benthic δ O values show significant glaciation occurred from 6.26 to 5.50 Ma, during which glacial-interglacial cycles were governed by the 41 kyr obliquity cycle. A major reorganisation of

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2912-579: The Late Cretaceous, are known from the Miocene of Patagonia, represented by the mole-like Necrolestes . The youngest known representatives of metatherians (the broader grouping to which marsupials belong) in Europe, Asia and Africa are known from the Miocene, including the European herpetotheriid Amphiperatherium , the peradectids Siamoperadectes and Sinoperadectes from Asia, and

3003-705: The Late Miocene, the Earth's climate began to display a high degree of similarity to that of the present day . The 173 kyr obliquity modulation cycle governed by Earth's interactions with Saturn became detectable in the Late Miocene. By 12 Ma, Oregon was a savanna akin to that of the western margins of the Sierra Nevada of northern California . Central Australia became progressively drier, although southwestern Australia experienced significant wettening from around 12 to 8 Ma. The South Asian Winter Monsoon (SAWM) underwent strengthening ~9.2–8.5 Ma. From 7.9 to 5.8 Ma,

3094-612: The Mediterranean refilled. That event is referred to as the " Zanclean flood ". Also during the early Miocene (specifically the Aquitanian and Burdigalian Stages), the apes first evolved, began diversifying, and became widespread throughout the Old World . Around the end of this epoch, the ancestors of humans had split away from the ancestors of the chimpanzees and had begun following their own evolutionary path during

3185-602: The Mediterranean, with mostly dry summers (except for scattered summer thunderstorms) and cold, wet winters. Snow can fall above 4,000 ft (1,200 m) elevation during frontal passages between November and April, but is most common in December through March. Annual precipitation totals are mostly in excess of 25 in (640 mm) on the coastal (southern) slopes above 3,000 ft (900 m) elevation, with up to 45 in (1,100 mm) falling in some areas above 5,000 ft (1,500 m). The coastal (south) side of

3276-574: The Miocene Epoch was mostly supported by the two newly formed biomes , kelp forests and grasslands . Grasslands allow for more grazers, such as horses , rhinoceroses , and hippos . Ninety-five percent of modern plants existed by the end of this epoch . Modern bony fish genera were established. A modern-style latitudinal biodiversity gradient appeared ~15 Ma. The coevolution of gritty , fibrous, fire-tolerant grasses and long-legged gregarious ungulates with high-crowned teeth , led to

3367-449: The Miocene. The largest form among them was a gigantic caiman Purussaurus which inhabited South America. Another gigantic form was a false gharial Rhamphosuchus , which inhabited modern age India . A strange form, Mourasuchus also thrived alongside Purussaurus . This species developed a specialized filter-feeding mechanism, and it likely preyed upon small fauna despite its gigantic size. The youngest members of Sebecidae ,

3458-550: The North American Great Plains and in Argentina . The global trend was towards increasing aridity caused primarily by global cooling reducing the ability of the atmosphere to absorb moisture, particularly after 7 to 8 million years ago. Uplift of East Africa in the late Miocene was partly responsible for the shrinking of tropical rain forests in that region, and Australia got drier as it entered

3549-616: The North American west coast. Like nearly all of the other mountains in the Transverse Ranges , the San Gabriels are a series of fault blocks that were uplifted in the Cenozoic . Tectonic uplift rates and erosion rates systematically increase as topography steepens eastward in the San Gabriel Mountains, where the San Andreas and San Jacinto faults meet. Current rates of erosion in the eastern San Gabriel mountains are among

3640-419: The Oligocene through the Miocene and into the Pliocene, the climate slowly cooled towards a series of ice ages . The Miocene boundaries are not marked by distinct global events but by regionally defined transitions from the warmer Oligocene to the cooler Pliocene Epoch. During the Early Miocene, Afro-Arabia collided with Eurasia, severing the connection between the Mediterranean and Indian Oceans, and allowing

3731-656: The Oligocene–Miocene transgression. As the southern Andes rose in the Middle Miocene (14–12 million years ago) the resulting rain shadow originated the Patagonian Desert to the east. Far northern Australia was monsoonal during the Miocene. Although northern Australia is often believed to have been much wetter during the Miocene, this interpretation may be an artefact of preservation bias of riparian and lacustrine plants; this finding has itself been challenged by other papers. Western Australia, like today,

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3822-617: The Qiongdongnan Basin in the northern South China Sea indicates the Pearl River was a major source of sediment flux into the sea during the Early Miocene and was a major fluvial system as in the present. During the Oligocene and Early Miocene, the coast of northern Brazil, Colombia, south-central Peru , central Chile and large swathes of inland Patagonia were subject to a marine transgression . The transgressions in

3913-622: The San Andreas Fault produces numerous springs, sag ponds, and wetland areas that are critical habitats for a variety of native species. Larger animals include California mule deer , California black bear , San Pedro Martir coyote and the rarely seen mountain lion or cougar. Smaller mammals include raccoons, opossum, skunk, and bobcats. Golden and bald eagles are found rarely, but hawks are common. Rattlesnakes are common and often encountered on trails by hikers. Critically endangered yellow-legged frogs have declined or vanished from

4004-497: The activity of the Columbia River Basalts and enhanced by decreased albedo from the reduction of deserts and expansion of forests. Climate modelling suggests additional, currently unknown, factors also worked to create the warm conditions of the MMCO. The MMCO saw the expansion of the tropical climatic zone to much larger than its current size. The July ITCZ, the zone of maximal monsoonal rainfall, moved to

4095-472: The aridity of the former. Unequivocally-recognizable dabbling ducks , plovers , typical owls , cockatoos and crows appear during the Miocene. By the epoch's end, all or almost all modern bird groups are believed to have been present; the few post-Miocene bird fossils which cannot be placed in the evolutionary tree with full confidence are simply too badly preserved, rather than too equivocal in character. Marine birds reached their highest diversity ever in

4186-638: The beginning of the Miocene, the northern margin of the Arabian plate, then part of the African landmass, collided with Eurasia; as a result, the Tethys seaway continued to shrink and then disappeared as Africa collided with Eurasia in the Turkish – Arabian region. The first step of this closure occurred 20 Ma, reducing water mass exchange by 90%, while the second step occurred around 13.8 Ma, coincident with

4277-649: The best sweet spots. On January 6, 1993, Echo Mountain, also referred to as Mount Echo, was delineated as part of the Mount Lowe Railway monument area listed by the U.S. Forest Service on the National Register of Historic Places . On top of the mountain are the ruins of "White City", a resort along the scenic Mount Lowe Railway , which could easily be seen from the valley below. From its point and down an incline to its foot in Rubio Canyon

4368-577: The course of this epoch . The youngest representatives of Choristodera , an extinct order of aquatic reptiles that first appeared in the Middle Jurassic , are known from the Miocene of Europe, belonging to the genus Lazarussuchus , which had been the only known surviving genus of the group since the beginning of the Eocene. The last known representatives of the archaic primitive mammal order Meridiolestida , which dominated South America during

4459-451: The end of the Miocene due to increased habitat uniformity. The expansion of grasslands in North America also led to an explosive radiation among snakes. Previously, snakes were a minor component of the North American fauna, but during the Miocene, the number of species and their prevalence increased dramatically with the first appearances of vipers and elapids in North America and the significant diversification of Colubridae (including

4550-422: The end of the Miocene. The Paratethys underwent a significant transgression during the early Middle Miocene. Around 13.8 Ma, during a global sea level drop, the Eastern Paratethys was cut off from the global ocean by the closure of the Bârlad Strait, effectively turning it into a saltwater lake. From 13.8 to 13.36 Ma, an evaporite period similar to the later Messinian salinity crisis in the Mediterranean ensued in

4641-429: The enigmatic Saint Bathans Mammal . Microbial life in the igneous crust of the Fennoscandian Shield shifted from being dominated by methanogens to being primarily composed of sulphate-reducing prokaryotes . The change resulted from fracture reactivation during the Pyrenean-Alpine orogeny, enabling sulphate-reducing microbes to permeate into the Fennoscandian Shield via descending surficial waters. Diatom diversity

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4732-461: The evolution of both groups into modern representatives. The early Miocene Saint Bathans Fauna is the only Cenozoic terrestrial fossil record of the landmass, showcasing a wide variety of not only bird species, including early representatives of clades such as moa , kiwi and adzebills , but also a diverse herpetofauna of sphenodontians , crocodiles and turtles as well as a rich terrestrial mammal fauna composed of various species of bats and

4823-499: The expansion of grasslands not to a CO 2 drop but to the increasing seasonality and aridity, coupled with a monsoon climate, which made wildfires highly prevalent compared to before. The Late Miocene expansion of grasslands had cascading effects on the global carbon cycle, evidenced by the imprint it left in carbon isotope records. Cycads between 11.5 and 5 million years ago began to rediversify after previous declines in variety due to climatic changes, and thus modern cycads are not

4914-653: The extinction of the last-surviving members of the hyaenodonts . Islands began to form between South and North America in the Late Miocene, allowing ground sloths like Thinobadistes to island-hop to North America. The expansion of silica-rich C 4 grasses led to worldwide extinctions of herbivorous species without high-crowned teeth . Mustelids diversified into their largest forms as terrestrial predators like Ekorus , Eomellivora , and Megalictis and bunodont otters like Enhydriodon and Sivaonyx appeared. Eulipotyphlans were widespread in Europe, being less diverse in Southern Europe than farther north due to

5005-789: The extreme eastern San Gabriels. The range terminates at Cajon Pass, through which runs Interstate 15 , and beyond which rise the even higher San Bernardino Mountains . The Range is bounded on the north by the Antelope Valley and the Mojave Desert and to the south by the communities of Greater Los Angeles . The south side of the range is almost continuously urbanized and includes the Los Angeles city communities of Sylmar , Pacoima , and Sunland-Tujunga , as well as cities and unincorporated areas of San Fernando , La Crescenta , La Cañada Flintridge , Altadena , Pasadena , Sierra Madre , Arcadia , Monrovia , Bradbury , Duarte , Azusa , Glendora , San Dimas , La Verne , Claremont , Upland , Rancho Cucamonga , Fontana , and Rialto . The north side of

5096-467: The fastest in the continental United States and have accelerated in response to the increased frequency of wildfires over the 1900s. Over future centuries, it remains unclear whether soil and brush ecosystems in the San Gabriel mountains will continue to re-establish soil and vegetation after increasing fire and soil-erosion frequencies, or if increasing fire frequencies and erosion will strip soils and permanently alter soil cover and vegetation types across

5187-437: The final Messinian Stage (7.5–5.3 Ma) of the Miocene. As in the Oligocene before it, grasslands continued to expand, and forests to dwindle. In the seas of the Miocene, kelp forests made their first appearance and soon became one of Earth's most productive ecosystems. The plants and animals of the Miocene were recognizably modern. Mammals and birds were well established. Whales , pinnipeds , and kelp spread. The Miocene

5278-421: The findings of marine invertebrate fossils of both Atlantic and Pacific affinity in La Cascada Formation . Connection would have occurred through narrow epicontinental seaways that formed channels in a dissected topography . The Antarctic Plate started to subduct beneath South America 14 million years ago in the Miocene, forming the Chile Triple Junction . At first the Antarctic Plate subducted only in

5369-402: The gorge is the southern "foothills" of the mountains, which rise abruptly 4,000 feet (1,200 m) above the Los Angeles Basin and give rise to the Arroyo Seco , a tributary of the Los Angeles River . Southeast of Big Tujunga Canyon, the southern front range of the San Gabriels gradually grows in elevation, culminating in notable peaks such as Mount Wilson at 5,710 feet (1,740 m). On

5460-430: The highest peak in the range at 10,068 feet (3,069 m). On the north slopes of the San Gabriel crest, the northern ranks of mountains drop down incrementally to the floor of the Mojave Desert in a much more gradual manner than the sheer southern flank. The Angeles Crest Highway , one of the main routes across the San Gabriels, runs through this area from west to east. Little Rock, Big Rock, and Sheep Creeks drain off

5551-411: The human lineage) appeared in Africa at the very end of the Miocene, including Sahelanthropus , Orrorin , and an early form of Ardipithecus ( A. kadabba ). The chimpanzee–human divergence is thought to have occurred at this time. The evolution of bipedalism in apes at the end of the Miocene instigated an increased rate of faunal turnover in Africa. In contrast, European apes met their end at

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5642-419: The interchange of fauna between Eurasia and Africa, including the dispersal of proboscideans and hominoids into Eurasia. During the late Miocene, the connections between the Atlantic and Mediterranean closed, causing the Mediterranean Sea to almost completely evaporate. This event is referred to as the " Messinian salinity crisis ". Then, at the Miocene–Pliocene boundary, the Strait of Gibraltar opened, and

5733-422: The lake levels of the Eastern Paratethys dropped as it once again became a sea. The Fram Strait opened during the Miocene and acted as the only throughflow for Atlantic Water into the Arctic Ocean until the Quaternary period. Due to regional uplift of the continental shelf, this water could not move through the Barents Seaway in the Miocene. The modern day Mekong Delta took shape after 8 Ma. Geochemistry of

5824-495: The mountain ecosystem. There are both areas of conifer as well as broadleaf forestation, including the presence of some endemic taxa. Conifer (pine, fir, cedar) and oak forests are most widespread above 5,000 feet (1,500 m) where the precipitation is above 30 inches (760 mm) (the central and eastern high San Gabriels). In the wetter areas, madrone and bay laurel trees also occur in places, and ferns are common. Trees like willow, alder, and cottonwood are also found throughout

5915-566: The mountains during big storms often produces flooding in adjacent foothill communities (especially in areas denuded by wildfires). The range is mostly smog-free above 5,000 ft (1,500 m) elevation, above the inversion layer. The large telescope installation at Mt. Wilson is a testimony to the clear atmospheric conditions that prevail, although light pollution from the L.A. basin below has hindered telescope activities in recent decades. The San Gabriel Mountains see wildfires frequently. The fires are often driven by dry Santa Ana wind events in

6006-425: The mountains is Angeles Forest Highway . Angeles Forest Highway begins 11 miles northeast of La Cañada Flintridge at its Angeles Crest Highway junction. Ending near Acton , it allows easy access to the central Forest and the fast-growing Antelope Valley . Because the "Forest" and the 11-mile (18 km) "Crest" portion leading to La Cañada Flintridge is well-traveled by Antelope Valley commuters, its road maintenance

6097-515: The north the range is abruptly dissected by the canyon of the West Fork San Gabriel River. Even further north the range slopes up into the towering main crest of the San Gabriels, a sweeping arc-shaped massif 30 miles (48 km) in length that includes most of the highest peaks in the range: Waterman Mountain , at 8,038 feet (2,450 m); Mount Islip , at 8,250 feet (2,510 m), Mount Baden-Powell , at 9,399 feet (2,865 m), Pine Mountain , at 9,648 feet (2,941 m), and Mount San Antonio ,

6188-496: The north, increasing precipitation over southern China whilst simultaneously decreasing it over Indochina during the EASM. Western Australia was at this time characterised by exceptional aridity. In Antarctica, average summer temperatures on land reached 10 °C. In the oceans, the lysocline shoaled by approximately half of a kilometre during warm phases that corresponded to orbital eccentricity maxima. The MMCO ended around 14 million years ago, when global temperatures fell in

6279-402: The northern part of the mountains, forming large alluvial fans as they descend into the Mojave. To the east, the San Andreas Fault cuts across the range, forming a series of long, straight, and narrow depressions, including Swarthout Valley and Lone Pine Canyon. South of Mount San Antonio, San Antonio Creek drains the mountains, cutting the deep San Antonio Canyon. East of San Antonio Canyon,

6370-523: The origin of many modern genera such as Nerodia , Lampropeltis , Pituophis and Pantherophis ). Arthropods were abundant, including in areas such as Tibet where they have traditionally been thought to be undiverse. Neoisopterans diversified and expanded into areas they previously were absent from, such as Madagascar and Australia. In the oceans, brown algae , called kelp , proliferated, supporting new species of sea life, including otters , fish and various invertebrates . Corals suffered

6461-463: The possible herpetotheriid Morotodon from the late Early Miocene of Uganda. Approximately 100 species of apes lived during this time , ranging throughout Africa, Asia and Europe and varying widely in size, diet, and anatomy. Due to scanty fossil evidence it is unclear which ape or apes contributed to the modern hominid clade, but molecular evidence indicates this ape lived between 18 and 13 million years ago. The first hominins ( bipedal apes of

6552-784: The preceding Oligocene and following Pliocene Epochs: Continents continued to drift toward their present positions. Of the modern geologic features, only the land bridge between South America and North America was absent, although South America was approaching the western subduction zone in the Pacific Ocean , causing both the rise of the Andes and a southward extension of the Meso-American peninsula. Mountain building took place in western North America , Europe , and East Asia . Both continental and marine Miocene deposits are common worldwide with marine outcrops common near modern shorelines. Well studied continental exposures occur in

6643-493: The range along with the stream courses (riparian habitat), even at lower elevations. Chaparral (dense shrub, brush, and small tree) vegetation is widespread where there is no continuous tall tree cover, especially at lower elevations. Chaparral is highly adapted to fire and replaces trees for decades after fires. There is a subspecies of the Leather Oak which is found only within the San Gabriel Mountains. The Rift Zone along

6734-482: The range gradually loses elevation, and the highest peaks in this section of the mountain range are in the south, rising dramatically above the cities of Claremont , Upland and Rancho Cucamonga . However, there are still several notable peaks in this region, including Telegraph Peak , at 8,985 feet (2,739 m), Cucamonga Peak , at 8,859 feet (2,700 m), and Ontario Peak , rising 8,693 feet (2,650 m). Lytle Creek , flowing generally southeast, drains most of

6825-437: The range is less densely populated and includes the city of Palmdale as well as the small unincorporated towns of Acton , Littlerock , Pearblossom , Valyermo , Llano , Piñon Hills , and Phelan . At the west end of the range lies the city of Santa Clarita . Within the mountains themselves are the small unincorporated communities of Mount Baldy , Wrightwood , Big Pines and Lytle Creek . Melting snow and rain runoff on

6916-634: The range just east of San Fernando, carrying runoff into the San Fernando Valley . Little Tujunga Canyon Road bridges the range in this area, connecting the San Fernando Valley to the Santa Clara River valley in the north. Towering over Big Tujunga Canyon north of Big Tujunga Reservoir , and south of Acton, is Mount Gleason, which at 6,502 feet (1,982 m), is the highest in this region of the San Gabriels. South of

7007-417: The range receives more precipitation than the desert (northern) side. The highest precipitation is found in the central and eastern parts of the range (Mt. Wilson to Mt. San Antonio). Annual precipitation totals are highly variable from year to year, and can be extremely high during wet El Nino years (sometimes over 70 in (1,800 mm), with single storm totals over 10 in (250 mm)). Runoff from

7098-722: The range which extends from the Cajon Pass (Interstate 15) on the east, where the San Gabriel Mountain Range meets the San Bernardino Mountain Range , westward to meet the Santa Susana Mountains at Newhall Pass (Interstate 5). South and east of Santa Clarita and north of San Fernando , the San Gabriel Mountains crest abruptly up to about 4,000 feet (1,200 m). Pacoima and Big Tujunga Canyons cut through

7189-564: The south side of the San Gabriels' highest mountains give rise to its largest river, the San Gabriel River . Just to the west of Mount Hawkins , a north-south divide separates water running down the two main forks of the river and their tributaries. The West Fork, beginning at Red Box Saddle, runs 14 miles (23 km) eastward, and the East Fork, starting north of Mount San Antonio, flows 18 miles (29 km) south and west through

7280-779: The southernmost tip of Patagonia, meaning that the Chile Triple Junction lay near the Strait of Magellan . As the southern part of Nazca Plate and the Chile Rise became consumed by subduction the more northerly regions of the Antarctic Plate begun to subduct beneath Patagonia so that the Chile Triple Junction advanced to the north over time. The asthenospheric window associated to the triple junction disturbed previous patterns of mantle convection beneath Patagonia inducing an uplift of ca. 1 km that reversed

7371-477: The streams due to the loss of suitable habitat. The introduction of invasive predators like trout, which feed on tadpoles, decimated their population. The main road that runs through the San Gabriel Mountains is the Angeles Crest Highway , State Route 2 . It starts in the southwest at the city of La Cañada Flintridge and ends at its junction with State Route 138 , just past Wrightwood , near

7462-544: The summer and fall. Notable wildfires in the San Gabriel Mountains have included the 2009 Station Fire , 2020 Bobcat Fire , and the 2024 Bridge Fire . Granitic and metasedimentary rocks are the primary constituent of the San Gabriel Mountains. Metasedimentary rocks were attached to the North American craton in the Precambrian eon, and granitic rocks formed throughout the Mesozoic as oceanic plates subducted underneath

7553-604: The west coast of South America are thought to be caused by a regional phenomenon while the steadily rising central segment of the Andes represents an exception. While there are numerous registers of Oligocene–Miocene transgressions around the world it is doubtful that these correlate. It is thought that the Oligocene–Miocene transgression in Patagonia could have temporarily linked the Pacific and Atlantic Oceans, as inferred from

7644-423: Was Allodesmus . A ferocious walrus , Pelagiarctos may have preyed upon other species of pinnipeds including Allodesmus . Furthermore, South American waters witnessed the arrival of Megapiranha paranensis , which were considerably larger than modern age piranhas . New Zealand 's Miocene fossil record is particularly rich. Marine deposits showcase a variety of cetaceans and penguins , illustrating

7735-624: Was a gradual and progressive trend of increasing aridification, though it was not unidirectional, and wet humid episodes continued to occur. Between 7 and 5.3 Ma, temperatures dropped sharply again in the Late Miocene Cooling (LMC), most likely as a result of a decline in atmospheric carbon dioxide and a drop in the amplitude of Earth's obliquity, and the Antarctic ice sheet was approaching its present-day size and thickness. Ocean temperatures plummeted to near-modern values during

7826-453: Was again considering plans to re-open the road, after pressure from local communities. In the winter, snowboarding and skiing are quite popular in the San Gabriels, at Mountain High and Mt. Baldy . The two other resorts, Mount Waterman and Kratka Ridge , are rarely open due to insufficient snow. In the summer, canyoneering , hiking, backpacking, picnicking, and camping are some of the activities popular with visitors. From time to time,

7917-464: Was arid, particularly so during the Middle Miocene. Climates remained moderately warm, although the slow global cooling that eventually led to the Pleistocene glaciations continued. Although a long-term cooling trend was well underway, there is evidence of a warm period during the Miocene when the global climate rivalled that of the Oligocene . The climate of the Miocene has been suggested as

8008-688: Was inversely correlated with carbon dioxide levels and global temperatures during the Miocene. Most modern lineages of diatoms appeared by the Late Miocene. There is evidence from oxygen isotopes at Deep Sea Drilling Program sites that ice began to build up in Antarctica about 36 Ma during the Eocene . Further marked decreases in temperature during the Middle Miocene at 15 Ma probably reflect increased ice growth in Antarctica. It can therefore be assumed that East Antarctica had some glaciers during

8099-646: Was most intense there. Around this time the Mi3b glacial event (a massive expansion of Antarctic glaciers) occurred. The East Antarctic Ice Sheet (EAIS) markedly stabilised following the MMCT. The intensification of glaciation caused a decoherence of sediment deposition from the 405 kyr eccentricity cycle. The MMWI ended about 11 Ma, when the Late Miocene Cool Interval (LMCI) started. A major but transient warming occurred around 10.8-10.7 Ma. During

8190-602: Was the Great Incline funicular of the Mount Lowe Railway, whose white cars could be seen ascending and descending Echo. Echo Mountain can be reached by the Sam Merrill Trail located at the top of Lake Avenue , or via the fire road which extends from Millard Canyon to a point along the old right of way, which will lead to the backside of the promontory. San Gabriel Mountains The San Gabriel Mountains ( Spanish : Sierra de San Gabriel ) comprise

8281-473: Was the most famous climbing area until it was closed for climbing. There are many other craggy areas scattered about the range that provide mostly traditional climbing opportunities. Angeles National Forest Fire Lookout Association has rebuilt and operates Vetter Mountain Lookout , and Slide Mountain Lookout . The organization is rebuilding South Mount Hawkins Lookout . Miocene As Earth went from

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