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Subsection M262Bg
San Gorgonio Mountains
The San Gorgonio Mountains area in Big Bear, known as Subsection M262Bg, covers the lower, warmer parts of the San Bernardino Mountains. It's nestled between the Mojave Desert to the north and the southern branch of the San Andreas fault to the south. Stretching from Cajon Pass to the Pipes Canyon fault, it features faults like the Mission Creek and Banning faults along its southern edge. This region experiences a warm to hot, moderately damp climate with some influence from the Pacific on its south-southwest side.
Geology
The area is rich in history, with most rocks dating back to the Mesozoic era, mixed with even older Precambrian rocks. There’s also a hint of marine sediments from the Paleozoic era and a smattering of younger, Pliocene sediments. The land’s sharp rises and steep cliffs are due to various geological shifts, and you’ll find a patchwork of sediments and alluvium along the way.Landscape and Soil
This mountainous region features steep slopes, narrow summits, and winding canyons, rising from around 1,500 to 6,000 feet. Soils are generally shallow and well-drained, lacking carbonates. They’re influenced by the local climate, with thermic temperatures at lower elevations and mesic temperatures on higher, north-facing slopes. Soil moisture stays pretty dry with a xeric regime.Vegetation
Plant life here is diverse, with shrublands and chaparral dominating the lower areas, while forests take over the higher ground. Lower elevations see chamise, live oak, and mixed chaparral, while higher elevations feature ponderosa pine and mixed conifer forests, with Jeffrey pines to the north.Vegetation by Type:
Climate and Water
Precipitation here ranges between 20-30 inches annually, with rain at lower elevations and snow higher up. Average temperatures span from about 45°F to 60°F, and the area generally enjoys around 200-250 freeze-free days. While streams flow fast when they’re full, most dry up by summer, and you won’t find any natural lakes here.------------------
This
subsection comprises the lower and warmer parts of the San Bernardino Mountains,
which are between the southern branch of the
San Andreas fault
on the south-southwest
and the Mojave Desert on the north. It extends from the
Cajon Pass
eastward to near the Pipes Canyon fault. It includes mountains between
the Mission Creek fault and the Banning fault on the south. The climate
is hot to temperate and subhumid. Marine effects on climate are moderate
on the south-southwest side and slight on the north and east sides of the
mountains. MLRA 20e.
Lithology and Stratigraphy. This subsection contains mostly Mesozoic granitic
rocks and Pre-Cambrian
igneous
and
metamorphic rocks. Also, there
is some Paleozoic marine sedimentary rock and minor amounts of Pliocene
nonmarine sediments. The mountains are a horst with faults and steep
escarpments on the south-southwest, east-northeast, and west-northwest
sides. Quaternary nonmarine sediments and Recent alluvium are small
but important components of the subsection.
Geomorphology. This is a subsection of steep and very steep mountains with narrow to rounded summits and narrow canyons. The subsection elevation range is from about 1500 feet up to 6000 feet. Mass wasting and fluvial erosion are the main geomorphic processes.
Soils. The soils are mostly shallow Typic Xerorthents, shallow Entic Haploxerolls, Entic Ultic Haploxerolls, and Mollic Haploxeralfs on granitic and Pre-Cambrian rocks and Lithic and Typic Xerochrepts on Paleozoic marine sedimentary rocks. On Recent alluvium and Quaternary marine sediments there are Typic and Mollic Xerofluvents and Ultic Argixerolls. Most of the soils are leached free of carbonates. The soils are well drained. Soil temperature regimes are thermic at lower elevations and on south-facing slopes, and some are mesic on north-facing slopes at higher elevations. Soil moisture regimes are xeric.
Vegetation. The predominant natural plant communities are Chamise series on shallow and very stony soils, Live oak chaparral shrublands, and Mixed chaparral shrublands at lower elevations and on south-facing slopes; Ponderosa pine series and Mixed conifer series at higher elevations; and Jeffrey pine series on the north side of the mountains.
- Characteristic series by lifeform include:
Grasslands: California annual grassland series, Desert needlegrass series.
Shrublands: Bigberry manzanita series, Bitterbrush series, Black bush series, California buckwheat series, California sagebrush series, Chamise series, Chamise - bigberry manzanita series, Chamise - Eastwood manzanita series, Chamise - hoaryleaf ceanothus series, Chamise - cupleaf ceanothus series, Chamise - white sage series, Chamise - black sage series, Chaparral whitethorn series, Cupleaf ceanothus - fremontia - oak series, Eastwood manzanita series, Fourwing saltbush series, Hoaryleaf ceanothus series, Scrub oak series, Scrub oak chaparral - whitethorn series, Interior live oak shrub series, Interior live oak - chaparral whitethorn series, Interior live oak - scrub oak shrub series, Interior live oak - canyon live oak shrub series, Mixed scrub oak series, Mulefat series, Scrub oak series, Scrub oak - chamise series, Scrub oak - chaparral whitethorn series, Scalebroom series.
Forests and woodlands: Birchleaf mountain-mahogany series, California juniper series, California walnut series, Coulter pine series, Coulter pine - canyon live oak series, Bigcone Douglas-fir series, Bigcone Douglas-fir - canyon live oak series, Black oak series, Canyon live oak series, Coast live oak series, Curlleaf mountain-mahogany series, Knobcone pine series, Interior live oak series, Jeffrey pine series, Mixed conifer series, Ponderosa pine series, Singleleaf pinyon series, Singleleaf pinyon - Utah Juniper series.
Surface Water. Runoff is rapid. All but the larger streams are dry through the summer. Natural lakes are absent.
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