OK, Students! Listen up and learn something new. Below is a guide
to the geology of the higher and cooler parts of the San Jacinto and the Cahuilla Mountains. The climate is temperate to cold, and subhumid; it is affected by elevation much more than by marine influence. Click here or hit your back button to return to the main San Jacinto Mountain page.

Lithology and Stratigraphy. The San Jacinto Mountains contain mostly Mesozoic granitic rocks and the Cahuilla Mountains contain mostly Pre-Cenozoic granitic and metamorphic rocks. Also, there are large areas of Pre-Cretaceous metasedimentary rocks and small areas of Pleistocene sediments.

Geomorphology. This subsection is on steep to very steep mountains with narrow to rounded ridges and narrow canyons, except where there are Quaternary fluvial landforms along the Hot Springs Fault and the San Jacinto Fault Zone. The subsection elevation range is from about 3000 feet up to 10,831 feet on Mount San Jacinto. Mass wasting and fluvial erosion are the main geomorphic processes.

Soils. The soils are mostly shallow Typic Xerorthents, Lithic Xerorthents, Typic Xerochrepts, Entic and Entic Ultic Haploxerolls, Argixerolls, Pachic Xerumbrepts, and Mollic Haploxeralfs. Soils on Pleistocene nonmarine sediments are mostly Haploxerolls. Calcium carbonates are leached from the soils. The soils are well drained. Soil temperature regimes are mostly mesic, and some are frigid at higher elevations. Soil moisture regimes are xeric.

Vegetation. The predominant natural plant communities are Ponderosa pine series and Mixed conifer series on the southwest side of the San Jacinto Mountains, Jeffrey pine series on the northeast side of the San Jacinto Mountains and on both sides at higher elevations, Lodgepole pine series at very high elevations, and Mixed chaparral shrublands at lower elevations. Canyon live oak series occurs in steep canyons. There is some Singleleaf pinyon series and California juniper series at lower elevations on the northeast side of the mountains. Characteristic series by lifeform include:
Grasslands: California annual grassland series, Desert needlegrass series, Sedge series, Quillwort series.
Shrublands: Big sagebrush series, Bigberry manzanita series, Bush chinquapin series, California buckwheat - white sage series, Chamise series, Chamise - cupleaf ceanothus series, Chamise -wedgeleaf ceanothus series, Chamise - white sage series, Deerbrush series, Eastwood manzanita series, Greenleaf manzanita series, Interior live oak shrub series, Interior live oak - chaparral whitethorn shrub series, Holodiscus series, Mixed scrub oak series, Mountain whitethorn series, Red shank series, Red shank - birchleaf mountain-mahogany series, Red shank - chamise series, Rothrock sagebrush series, Scrub oak series, White sage series.
Forests and woodlands: Bigcone Douglas-fir series, Bigcone Douglas-fir - canyon live oak series, Birchleaf mountain-mahogany series, Black oak series, California juniper series, Canyon live oak series, Coulter pine series, Coulter pine - canyon live oak series, Curlleaf mountain-mahogany series, Coast live oak series, Incense-cedar series, Interior live oak series, Jeffrey pine series, Limber pine series, Lodgepole pine series, Mixed subalpine forest series, Mixed conifer series, Parry pinyon series, Ponderosa pine series, Singleleaf pinyon series, White fir series.

Climate. The mean annual precipitation is about 16 to 30 inches. It is mostly rain at lower and snow at higher elevations. Mean annual temperature is about 40 to 58 Deg F. The mean freeze-free period is about 150 to 225 days.

Surface Water. Runoff is rapid, except from nearly level alluvial plains. All but the larger streams are dry through the summer. There are no natural lakes.