San Jacinto Mountains showcase extraordinary geology

• In slightly less than seven horizontal miles the peak rises from 800 to 10%2C834 feet above sea level
• No other mountain in the lower 48 states rises so high so fast
• The peak will continue to rise%2C though at a rate no human will witness

The most impressive natural feature in the Coachella Valley is the northeast face of San Jacinto Peak. In slightly less than seven horizontal miles the peak rises from 800 to 10,834 feet above sea level, creating the steepest escarpment in the continental U.S. No other mountain in the lower 48 states rises so high so fast, not even the Sierra Nevada or Grand Tetons.

The San Jacinto Mountains are part of what geologists term the Peninsular Ranges Province, one of the largest geological units in North America. Beginning in Mexico at the tip of the Baja Peninsula, the province runs northwest for 900 miles and finally terminates with the San Jacinto Mountains of Southern California. Only the province's northernmost 120 miles extend into the United States.

The San Jacinto Mountains fall totally within the confines of Riverside County and are approximately 100 miles east of Los Angeles.

Although San Jacinto's peak is the highest point in the province, it is not the only peak that exceeds 10,000 feet in elevation. Thirteen peaks within the San Jacinto Mountains rise above the 10,000-foot level, including Jean Peak (10,570 feet), Miller Peak (10,400 feet) and Marion Mountain (10,362 feet). The total land area exceeding 10,000 feet covers approximately 1.5 square miles.

The rock mass of the San Jacinto Mountains is classified as Mesozoic granite. It is a light-colored igneous rock that can be easily observed anywhere in the San Jacintos at intermediate to high elevations. This granite resulted from the cooling of magma moving towards the surface about 100 million years ago during the Mesozoic Era, the age of dinosaurs. This granite is called a batholith and it formed the core of the Peninsular Ranges Province that we know today. For tens of millions of years the batholith remained many miles beneath the earth's surface.

Slowly, the batholith began to rise as the rock above eroded, like a ship rising in the water while emptying its heavy cargo. Around 30 million years ago enough of the overlying rock had eroded to allow the batholith to rise above sea level and expose its upper portions.

When a crack formed in the crustal plate approximately 20 million years ago, the Peninsular Ranges Province and the San Jacinto Mountains rose at a relatively rapid rate. Known today as the San Andreas Fault, the crack eventually spread to form a boundary between two huge portions or plates of the earth's crust: the Pacific Plate and the North American Plate.

Movement of the earth's plastic like interior caused the two plates to slide past each other at the fault.

Although most of the movement was horizontal, some was vertical, as a result of the plate edges snagging and colliding.

We know that the rise took place comparatively rapidly, particularly in the last 5 million years since the scarp is so high -- the highest in all of continental U.S. Today it's safe to assume that the peak will continue to rise, though at a rate no human will witness.