[pct-l] Geology of Nth Side of San Jacinto

[Bighummel at aol.com (Bighummel@aol.com)]

The guidebook notes, as you descend the north side of San Jacinto, that "To 
your northeast the confused alluvial terrain beyond San Gorgonio Pass attests 
to recent activity along the San Andreas Fault."

Actually, this view is very, very cool from a geologist's point of view.  The 
base of the foothills in the distance form a very straight line, which is the 
Mill Creek Fault, a major splay of the San Andreas Fault.  The base of the 
foothills in your foreground, i.e. the base of San Jacinto on the north, is the 
Southern San Andreas Fault.  This fault can be traced by a thin line of green 
vegetation in the desert, perpendicular to Snow Creek, and can be seen to 
offset this creek and another to the right.  The San Andreas fault is a right 
lateral fault, i.e. the other side of the fault is moving to the right of your 
position, regardless of which side of the fault you are standing on.  Many creeks 
that cross the San Andreas are right offset.

These two faults join together just to the west and combine to form a single 
San Andreas fault that the trail crosses at Cajon Pass.  Hiking north you 
cross the San Andreas fault at San Gorgonio Pass, at Cajon Pass and north of Agua 
Dulce; three times. 

If you happen to feel a shaken while you're out there hikin, then feel 
fortunate that you are there and not in some high rise building or in front of a 
brick building, or glass faced building.  Dance on the earth ripples and waves 
and sing a praise for Saint Andreas!!!!!

Greg "Strider" Hummel

"Saint Andreas, deliver us from our faults!"