Wednesday, March 17, 2021

Box Canyon and Painted Canyon Along California's San Andreas Fault

Painted Canyon in the Colorado Desert of California 

I recently visited the Colorado Desert in Anza-Borrego State Park, California, where I met up with friends to explore the backcountry. On the way to the park, we hiked in Painted Canyon, located adjacent to the San Andreas fault and where young sediments have been crumpled by the fault movement. Once inside the Park, we hiked in Borrego Palm Canyon, Indian Canyon and the Valley of The Thousand Springs. Along the way, we saw evidence for ancient Lake Cahuilla. There is much to see in this part of the world.

View to the west along the Box Canyon Road off of Interstate 10. These Pliocene and Pleistocene strata have been deformed as the San Andreas fault causes rocks on either side to become compressed.

Entering Painted Canyon as it slices through the Pliocene and Pleistocene Palm Springs Formation. These sediments were derived from local granite outcrops and were deposited in a non-marine alluvial setting as the San Andreas fault opened up a basin. This is within the Mecca Hills Wilderness Area (BLM land).

The young sedimentary rocks are underlain by unnamed Proterozoic gneiss and migmatite rocks. Here you can see the obvious unconformity as we walk up the canyon. Note the topography cut into the crystalline rocks below and filled with sedimentary debris.

Around the bend in the stream bed, the contact is seen dipping down so that we can get a better look.

Sure enough, this really Great Unconformity is right there for us to see and touch. The difference in age between these these two rocks is no less than 500 million years and may be over 1800 million years. 

The textures in the old rocks was truly spectacular.

There are a few knickpoints in the stream bed but ladders are installed to get around them. 

Just above the contact of the two rock units are conglomerate lenses where small channel fills left pebbles and cobbles.

What a lovely hike and if you find yourself in Joshua Tree National Park nearby, I can recommend a hike in Painted Canyon and a drive in Box Canyon.

NOTE: This Wilderness area is adjacent to a very large population near Palm Springs and in the agricultural Coachella Valley. Therefore, it is constantly under threat from activities that may be considered non-compliant with Wilderness values elsewhere. As our society grows and multiples, many of our protected areas will come under similar threats. However, I believe that we must encourage and include wider and larger constituencies for the outdoors in general and Wilderness in particular. Some of the people we saw in this canyon were not "typical" Wilderness users with Columbia shirts and hiking pants. Yet they were enjoying the resource in appropriate ways. I add this note to begin a discussion on how we can grow larger constituencies for Wilderness values!