The term "high sierra" relates to alpine areas above the main forest zone at 8000' elevation and above. The land is characterized by glacier- carved open peaks and basins. 100 million years ago vast amounts of molten granite were injected into and under the overlaying strata and crystallized into a huge mass of solid granite. The forces of erosion over time began to expose the granite. 60-70 million years ago, this granite mass was uplifted on the east side, creating a steep eastern and gentle westward slope. A series of volcanic flows covered portions of the central sierra. Beginning about 12 million years ago, the entire range was uplifted several thousand feet along the faults of the eastern flank. The increased grade accelerated the cutting action of westward flowing streams. As the crest of the sierra was thrust above snowline, glaciers formed, sculpting the high country, mostly during the last 1 million years. This area, received great supplies of moisture-laden air from the Pacific and a large ice cap formed. Only the highest peaks protruded from this mass. 1500-foot thick glaciers sculpted the sides of these mountains and canyons below as they slowly advanced.

Today most of the prominent peaks within the Byway corridor are remnant volcanic flows that stood above the glaciers. They have successfully resisted erosion for millions of years. The valleys below generally were scoured to the granite bedrock. This is apparent at Lake Alpine and many other locations where volcanic bluffs form the skyline with sculpted granite bedrock in the foreground. Evidence of the glaciers exist along the roadside near Big Meadow. Huge boulders were stripped from the highcountry and plowed to the side as the glacier advanced. These "erratics" litter both sides of the highway through this zone. They now rest more than 1000' above the river that was filled with icy debris to this level. The last glacier ended its advance creating a terminal moraine in the Arnold area about 13,000 years ago.

The Sourgrass Slide
Sourgrass Slide Brochure by Richard Petersen (large download : 1.27mb)		...One of these glaciers dropped some of its icy load (moraine deposit) thousands of years ago, near Dorrington, forming summit level ridge. On New Year's Day in 1997 these unconsolidated "moraine" deposits soaked up all the rain and snowmelt water possible during an unusually wet winter. The rain kept falling but the mountain could no longer absorb more water. Then gravity took over. An estimated 20,000 cubic yards of material slipped out of the ridge and flowed downhill. The flowing ooze crossed the highway and swept the entire forest within its 100' - 500' wide path. Two miles later an estimated 250,000 cubic yards crashed into the raging North Fork of the Stanislaus River. Up to 23" of soil had been stripped to bedrock. The 250' long bridge at Sourgrass was ripped from its footing and flipped onto the opposite shore in twisted pieces. The upper mile of the slide is within clear view of the Highway, 3 ½ miles east of Dorrington.

© 2003 - 2008 Ebbetts Pass National Scenic Byway Web Committee | Terms of use
The Groundspeak Geocaching Logo is a trademark of Groundspeak, Inc. Used with permission.