Color, Canyons and Adventure: Hike Coffee Bean Canyon on the San Andreas Fault

Hike Distance: 12.3 miles

Elevation Gain: 1,177 feet

TrailsNH Hiking Difficulty Calculator: 170 – Strenuous

Click here to navigate to the TrailsNH website for a description of the hiking difficulty calculator

Our original plan for today was to hike in several side canyons located along Box Canyon Road. Unfortunately, as we approached the hills there were detour signs posted that Box Canyon Road was closed as a result of flooding from a heavy rainstorm the previous week. We quickly discovered an alternative hike in Coffee Bean Canyon located in the western Mecca Hills.

The trailhead is located on a dirt road at the entrance to an aggregate company. A gate blocks access to the trail and it's a 2-mile walk form the gate to the actual entrance to the canyon. The road parallels the Coachella Canal that provides irrigation to the farm lands of the Imperial Valley. The Colorado River is the source for water in the canal. It's a strange sensation to walk along the trail with farm lands of Mecca on one side...

and the Mecca Hills on the other side.

Even in the western hills there were sign of the recent heavy rains.

We left the dirt road that ran along side the canal and began walking through a wash that led to the canyon.

Once inside the canyon, the walls began to gradually rise on either side.

The Mecca Hills were formed by movement along the San Andreas Fault Network, but that is not the only fault that has made its mark on the area. Several faults split the region, and in Painted Canyon, the San Andreas Fault is actually the least visible fault, but its effect on the landscape is clearly evident.

Along this section of the San Andreas Fault System, the intense heat and pressure of tectonic plate movement twisted and contorted these rocks as if they were Play-doh. Look closely, you can see a 45° or more shift or folding of rock. These rock layers were originally laid down horizontally and then plate movement compressed them and caused them to fold into an almost vertical stack.

In this rock face the almost arch-shaped folds are visible in the center of the picture below.

The unofficial name sake for this canyon came into view.

The hills exhibit a 'coffee bean' color. The red sediment is red fault gouge, a clay-like substance that forms where the North American Plate grinds against the Pacific Plate. This movement not only crushes the rocks along the fault but also pulverizes them into sand-sized grains. The color arises from iron minerals interacting with the fault gouge. Consider the red layer as tectonic rock flour produced by millions of years of grinding.

As the rocks are pulverized on either side of the fault, they are pushed up to the surface until it formed hills of fault gouge. The gouge began forming within the last 1-2 million years but the visible red gouge is probably only tens or hundreds of thousands of years old.

It wasn't a loose covering of sediment. Dave easily climbed this hill without the gouge crumbling under his feet.

We exited from the canyon and continued following the main wash.

The surrounding Mecca Hills to our east and north were beautiful even in late morning sun. These hills were formed as recently as one million years ago by compression forces from movement along the San Andreas Fault System. Mecca Hills offer one of the best locations for viewing the complex folding and faulting that occurs along the San Andreas.

While the surrounding mountains (Little San Bernardino and Orocopia Mountains) are primarily old granitic rocks, the Mecca Hills are young sedimentary rocks.

Looking back at the wash and Coffee Bean Canyon,

We followed the wash southeast past several side canyons and then veered to the left after the first major split. This large side canyon looked promising and worth a visit. See the map at the end of this blog for a satellite view of our path into the side canyon.

During fault system movement, the weak sedimentary rock beds were shoved tightly against the bedrock of the Orocopia Mountains to the east.

Something had to give and the weaker sediments collapsed into folds. As seen in the picture below, the sediments were compressed and uplifted so that they buckled and faulted into many tightly compressed near-vertical folds stacked on top of each other.

The softer sedimentary rock is more easily eroded by wind and water.

The canyon began to narrow.

Dave was very trusting considering we are hiking along the San Andreas fault. Pretty amazing the boulder fell from above and got jammed between the side walls.

We were no longer following a wash but rather a narrow drainage gully.

Climbing over rock falls from the canyon wall.

We arrived at the point where we needed to turn back. At the end of this narrow passage, there was a notable drop. Opting to explore this side canyon had been a wise choice!

We retraced our steps to the main wash. There was another side canyon we had noticed earlier in the hike that we wanted to explore.

The relatively healthy looking palm was a sign that groundwater was percolating through the faulted rocks to nourish this plant.

The canyon narrowed quickly.

Soon we were climbing around, over and under rock piles.

Notice how this rock has split perfectly, with smooth surfaces on both sides. It appears as though it was cut by human hands, but in reality, nature intervened, splitting the rock along its weakest plane where layers were compressed under intense pressure and temperature.

In the canyon, we found a great example of rock layers deformed by pressure from tectonic plate movement. The pressure created an anticline fold.

Times flies when you're hiking in the Mecca Hills. There is so much to distract you, but it was time to head back to the car. We retuned to the main wash.

Heading back through Coffee Bean Canyon.

What began as an 'alternative' hike this morning turned into an incredible journey through the western Mecca Hills. I highly recommend this hike.