Talus (or Scree)
(c) 2003 Andrew Alden, licensed to About.com, Inc. (fair use policy)
Talus, or scree, is the accumulation of broken rock that lies on a steep mountainside or at the base of a cliff. If you're writing a geologic paper, talus is the preferred term, but scree is more fun to say. This example is near Mount Baldy in the eastern San Gabriel Mountains of southern California.
The rocks here are largely granite blocks from large rock bodies that have been rapidly uncovered by tectonic uplift and intense erosion. The high altitude promotes weathering of the exposed bedrock by repeated freezing and thawing, a strong daily thermal cycle, and the kind of pressure-release jointing found throughout the young California mountains. So clean rock crumbles into steep piles and talus slopes like this before its minerals can alter into clay minerals. That comes much later, after the talus is washed and tumbled downhill, turning to alluvium and eventually into soil and sediment.
A talus slope is dangerous terrain. The material is sitting at its steepest possible slope—its angle of repose. A small disturbance, such as your misstep, can trigger a slide that may injure or even kill you as you go downhill with it. Also, there is no geological information to be gained from walking on scree.
Another picture of talus is available as a free wallpaper image.
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