A magnificent display of erosion can be seen here looking out across the valley to the west. The underlying geology of this area (referring to Chino Hills State Park) is part of the Puente Formation, sedimentary rock that is sometimes exposed like in the ridges to the west. Currently we are standing in the north tip of the Santa Ana Mountains, which contain the highest point in Orange County (Santiago Peak). In terms of the Puente Formation, we are located in the southeast end.
The blue circled portion in the map is our apporximate location in terms of the Puente Formation (it is not exact). From the legend, it is concluded that the underlying rock is mainly sandstone. This formation interrupts the generally flat Los Angeles Basin with a variety of rolling hills, mountains and canyons on its south and east sides. The hills are a result of uplift and folding along the Whittier and Chino faults.
Erosion
Erosion is the breakdown and removal of rock by exogenic processes. Exogenic, meaning outside, explains that erosion is caused by outside processes, like wind of water flow. Not to be confused with weathering, erosion, breaks down the rock or soil, and transports it to a different location. When it is done being moved, the leaving-behind of the rock is called deposition. Eroded sediment may be transported a few millimeters, of for many hundreds of kilometers. We can see to the west the line of multiple ridges that have been eroded. Heading in the direction of the ridges, one would descend into Fremont Canyon, where some of Orange County's highest wind speeds have been recorded.
You've hiked all the way here, now claim this earthcache as a find!
Send an email with the text GC5HJNV Effects of Erosion upon Sandstone -- Coal Canyon on the first line, and the answers to the questions:
1) How many distinct ridges can you spy out to the west?
2) How do you suspect these ridges were eroded (wind, water, or something other)?
Sources:
1) http://en.wikipedia.org/wiki/Exogeny
2) http://en.wikipedia.org/wiki/Erosion
3) http://www.everytrail.com/destination/chino-hills-state-park
4) http://www.newuniversity.org/2009/05/features/mines_mountain_lions_and192/
5) http://www.nps.gov/parkhistory/online_books/geology/publications/bul/845/sec29.htm
Enjoy your hike!