Discover the Thrills of Cave Exploring Along the San Andreas Fault

Without a doubt the Mecca Wilderness and now Chuckwalla National Monument is our favorite place to hike in Southern California. We first visited this area in 2017 and return here often for its unparalleled beauty and limitless hiking opportunities. From peaceful desert washes to exciting slot canyons this region formed by the destructive power of the San Andreas Fault network has something for everyone.

The Mecca Hills Wilderness was created in 1994 when the U.S. Congress designated 26,356 acres in the Mecca Hills to be overseen by the U.S. Bureau of Land Management (BLM). The BLM manages designated wilderness areas to protect their wilderness character, restricting motorized vehicles, mechanized equipment, and other activities that could harm the environment. While preserving the natural state of the areas is paramount, BLM wilderness areas also provide opportunities for recreation, scientific research, and other activities that are compatible with the wilderness environment.

In January 2025 the Mecca Wilderness and an additional 600,000+ acres were further protected when President Biden signed a proclamation establishing the Chuckwalla National Monument (CNM). This signing culminated a multiyear effort federal, state and local groups as well as the members of the Tribal Nations to further preserve and protect these federal lands for future generations.

Within the National Park system, a National Monument is a protected area, often on federal land, established to preserve significant cultural or natural features, including historic sites, prehistoric ruins, and objects of scientific interest. For anyone who has studied the area encompassed within this monument, certainly meets this basic definition. The map below outlined the boundary of the CNM. It is one of the largest national monument by acreage in the US.

Dave and I continue to explore here and educate family, friends and others about the value of these lands. To that end, we have been leading Friends of the Desert Mountain (FODM) guided hikes in these lands since 2024 and helped to introduce hundreds of people to the CNM.

Cave Exploring Along the San Andreas Fault

Although the Grotto No 1 hike is not a trail we would offer to FODM participants, it is certainly one that we enjoy and offer as an option for our more adventurous family and friends. The Grotto No. 1 hike is a double lollipop trail that takes you through washes, canyons, and a cave (grotto) created by a combination of plate tectonics and erosion over hundreds of thousands of years. Let's begin our cave exploration.

Hike Distance: 8.8 miles

Elevation Gain: 1,125 ft elevation gain

TrailsNH Hiking Difficulty Calculator: 141 – Moderately Strenuous

Click here for a review of prominence and its role in mountain topography

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

IMPORTANT UPDATE: As of January 2024, access to the grotto is blocked due to debris flows caused by the tropical storm in August 2023. Before offering this hike as a private excursion for Friends of the Desert Mountains, I walked the trail. I hiked counterclockwise to the 'exit' but was unable to pass through the debris. I've included some photos in the blog illustrating how the storm has changed the trail. We’ll continue hiking here but will be limited to exploring the trail to and from the oases.

Starting on the Ridge Trail

The empty off-road 'parking lot' indicated that for this midweek hike, we would be on our own when it was time to explore the grotto.

The trail began by following a wash that led to the tops of these hills. The Mecca Hills, located on the northeast side of the Coachella Valley, were formed due to the continuous collision between the North American Plate and the Pacific Plate along the San Andreas Fault network. Notably, the San Andreas Fault is not the sole fault that has shaped the landscape in these hills.

As the Pacific and North American plates slide against one another along the San Andreas Fault, certain segments of the fault sometimes overlap and connect. This forms a "block" of earth between the two plates, known as a restraining bend. The Mecca Hills is one such block, which is being uplifted and compressed due to the pressure from the moving plates. Similar uplifted fault zones have led to the formation of Durmid Hills and Indio Hills. It's not a coincidence that these hills (circled in purple) all align with the San Andreas Fault (the red dashed line running diagonally from the bottom right to the top left).

After reaching the hilltops, we walked along a ridge line for half a mile. Because the hills lack significant alluvial cover or vegetation, the rocks and their distinct structure are prominently exposed and easily seen. This clear view of 3-5 million years of tectonic plate destruction is a key reason why geologists and seismologists have extensively studied the Mecca Hills Wilderness.

Soon, we were greeted with remarkable views of the Salton Sea just above the hilltops. For further details about the iconic Salton Sea, explore the blogs on Walking on Volcanic Domes in the Salton Sea and History of the Salton Sea.

Eventually, the trail gently descended several hundred feet to the Hidden Springs Canyon Wash. This rugged and contorted landscape reveals a 0.75-mile-thick sequence of sedimentary rock layers accumulated over millions of years. These layers have been repeatedly turned, elevated, and altered by fault movements in these hills.

Unfortunately, not all the trails today will be as clearly marked or obvious as this section leading down to the wash.

Walking in the Wash

Monsoon rains and winds continually alter this landscape through erosion. The evidence of fallen hills was apparent on both sides of the wash. The difference in 'resistance to erosion' among the different layers results in unique formations, such as the more durable dark-colored cap on these hills. The caps erode slower then the less durable light brown layers.

The sandy wash of Hidden Spring Canyon was dotted with palo verde trees, smoke trees, and various other low desert shrubs. At this point it was hard to imagine that we'd be cave exploring on this trail.

The Costa's Hummingbird is characterized by a green body and an iridescent violet crown and throat patch which is visible in this photo. It was hanging out in the wash bushes.

The wash started to narrow, and the walls gradually rose upward.

Weston and Mackenzie found shade beneath the flowering palo verde tree; it was the last shaded spot we would encounter before reaching the grottos. The term 'palo verde' translates to 'green stick' in Spanish. This name is fitting because every part of the tree, from its leaves to its branches and trunk, is green. Unlike most trees, a palo verde can perform photosynthesis through its bark, a process typically confined to leaves in most plants. These trees are exceptionally well-suited to the desert environment and are among the most drought-resistant trees. An interesting fact: the seed pods and flowers of the palo verde are edible. We haven't tried them yet, but perhaps next time we will.

Specific colors in the rock layers contribute to the amazing colors in the canyon walls.

Approximately 1.8 miles in, we came upon a reddish-brown sandstone gate that opened to our left. The opening appeared to have been carved out, creating a clear path for adventure seekers.

The canyon walls consist of the 'Palm Springs Formation', a sedimentary rock layer formed during the Pleistocene Era (2,580,000 to 11,700 years ago). Over time, sediment from the erosion of nearby mountains and runoff from the ancestral Colorado River accumulated here, layer upon layer. The immense weight of each new layer compressed the sediments, expelling water, and chemical processes then acted to 'cement' the sediments together, creating sedimentary rock layers. The following photo shows multiple layers of these sedimentary rock strata.

Debris from rock falls in the upper layers formed several narrow passages along the trail. These sedimentary conglomerate rocks consist of rounded or angular rock fragments bound together. The plant debris near Dave's feet resulted from fast-moving waters that uproot plants, causing them to gather at 'choke points' like these tight spaces. Squeezing through these openings was a challenge not quite cave exploring in the grottos but it was still fun.

Less than a quarter of a mile after passing through the 'gate' we arrived at Hidden Spring Oasis. From the looks of these Washingtonia filifera, the oasis is providing sufficient water to maintain this small but thriving grove. Unlike most desert plants that adjust to life with very little water, palm trees thumbs their nose at water conservation. Their roots barely reach down 8-12 feet, so they can only grow where there is a reliable and abundant source of water at or near the surface.

These palms can reach heights of up to 59 feet and generally have a lifespan of 80 to 250 years. The distinctive feature that sets these palms apart from other palms commonly seen in California is that when their fronds die, they stay attached and hang down, forming a broad skirt around the trunk. This skirt offers shelter to various small mammals, birds, and desert reptiles, such as rattlesnakes. A word of caution—never insert your hand into a palm skirt.

During our initial hike on this trail in October, we noticed a small pool of stagnant water within the palm grove. Groundwater seeps through fractures in the rocks and sediment along the Hidden Springs Fault that traverses this region. Even small pools like this are vital for the survival of the animals inhabiting the Mecca Hills.

Photographed in 2022, this palm seedling just a few inches high symbolizes a promising outlook for the future. Experts suggest that with adequate water, the germination and survival of seedlings only need to happen once every hundred years to sustain a palm oasis. Perhaps we'll have the chance to monitor this 'little guy' in the coming years.

By 2025, the palm had grown significantly.

Numerous ocotillos were flourishing at the edge of the oasis. These sizable shrubs, characterized by their long, cane-like spiny stems, are more closely related to tea and blueberry bushes than to cacti.

When there is sufficient moisture, small bright green leaves, measuring 1-2 inches, emerge from the thorny stems.

Even though the trail vanished after the oasis, we knew that it continued along the top of this ridge.

It was a matter of surveying the hillside to identify the 'best gully' to climb out.

Once on top, looking back we had a bird's eye view of Hidden Spring Oasis and the uplifted layers of the Mecca Hills that dip toward the valley and the San Andreas Fault.

Appreciating the views from atop the ridge.

At first, the trail hugged one side of the canyon wall to our left. In several spots, substantial erosion made progress slow.

Eventually, the path turned eastward, leading to a succession of rolling hills. It looked like a moonscape; it was desolate and rocky, with no one around.

We approached our next waypoint, Hidden Spring Canyon, which emerged on our right. Dave started searching for a route into the canyon. As we drew nearer, the trail became less defined until it eventually vanished among the rocks and debris.

After trekking over 3 miles, Dave located the 'best gully,' and we made our way down into the canyon. Luckily, the trail wasn't as challenging as the picture suggests.

Even with the shallow canyon walls, we were treated to our first break from the scorching sun since the palo verde tree. Rubble and rock-fall debris littered the canyon floor.

Despite the shallow canyon walls, we were temporarily out of the blazing sun. The canyon floor was scattered with rubble and rock-fall debris.

Although the sidewalls didn't rise to create a 'slot canyon' the trail narrowed considerably.

Dave was dwarfed by debris which became larger the further down canyon we traveled. Notice the size of the boulders embedded in this conglomerate

At this point, the canyon walls were towering over us. The incredible landscape and fascinating geology are what motivate us to hike and explore the Mecca Hills. Few places in Southern California provide this combination of 'fun' elements.

It's hard to grasp the power of the moving water that created this stream-cut slot canyon. Imagine monsoon rains rushing through an initial fissure in the ground a few hundred thousands years ago that slowly eroded this canyon, cutting deeper and deeper without expanding the area between the walls.

This photo was Dave's idea. 'Go stand under that multi-ton rock that's wedged between the walls, it will be a great shot.'

Notice how the right side of this rock debris is nearly straight. At one point, it cleaved perfectly from the canyon's side-wall, dropped to the ground, yet somehow stayed whole as a single rock structure.

More fun squeezing through tight spaces. We were lucky and could squeeze through without removing our packs, unlike other hikes where we weren't as lucky. The angular rock fragments or clasts in the conglomerate suggest they formed nearby, since rounded clasts typically result from long-distance travel. These conglomerates look like poorly mixed concrete, with the large clasts providing excellent hand and footholds.

If you look closely in this photo, you can see at least two distinct episodes when monsoon rains raced trough this area. Each event is marked by a layer of large clasts with smaller clasts and fine sediment edged between. Initially, the swift water carried and deposited large clasts, but as the flow slowed down, only smaller clasts and eventually just sediments were left to settle. This process repeated multiple times, creating a new layer with each event.

After trekking nearly 4 miles, we arrived at the grotto (opening, bottom left of center) and began our cave exploration adventure.

We put on our headlamps and stepped into the darkness. Starting on level ground for the initial few feet helped us adjust to the dim lighting.

Dave led the way, stepping up and over boulders projecting from the conglomerate walls of the grotto/cave.

Dave captured this photo while I navigated using the 'stepping stones' to avoid squeezing through the tight opening at ground level.

Can you picture yourself in Hidden Spring Canyon or, even more daunting, in these caves when monsoon rains or thunderstorms sweep through the area? While unexpected rain events are rare in Mecca, we always review the weather forecast before hiking in the Hills. If we encounter conflicting information, we immediately consult the National Weather Service site. There are several excellent sites that offer information on the hazards of hiking in slot canyons—be sure to check them out before you go.

We had to crawl to leave the grotto through this opening. However, our cave exploration was far from over.

This is a photo taken while looking up at the ceiling as we exited the grotto. Enormous rocks, as large as houses, were lodged between the walls. I've also included a photo from outside that more clearly shows the 'unusual' placement of these rocks.

The end in sight.

Here are the faces of happy hikers. Weston and Mackenzie are always ready for a tough hike, and we still had more distance to travel.

Movement along the fault zone and local erosion has resulted in rocks being precariously wedged between the walls of the canyon. It doesn't take a seismologist to recognize that strong shaking during an earthquake could potentially loosen and topple these rocks.

These are the same rocks that were photographed looking up at the grotto ceiling. If it makes you feel any better, a picture taken at this exact location almost 25 years ago shows no new significant cracks in the canyon walls and very little rock movement in the grotto opening.

The photo below was taken in 1996.

We were treated to another small cave to explore before leaving the grotto area.

There were small gaps above, eliminating the need for headlamps.

At the end, we had to perform a combination of stepping up and twisting around these overhead boulders to reach the cave exit.

No doors on this grotto hike, just more tight spaces to navigate through.

Two small ladders were the last obstacle we faced.

A short jump or climb down and we were back on the canyon floor.

UPDATED JANUARY 2024: The exit from the grotto is no longer accessible. In the photo below, it's evident that 4-5 feet of sand has built up around the exit. This is especially visible in the rocks that Dave is climbing down—they are now barely visible. In addition, the opening below the triangular shaped rock is significantly more narrow and filled with sand, rock and debris. There are other signs of massive erosion. There is a large square shaped rock at the top of the canyon (phot above) that is missing in the January update. Erosion probably caused the rock to fall into the grotto canyon opening. Who knows when or if this trail will be useable as a loop.

I tried multiple times to climb through the debris and get to the grotto, but there was no sign of the trail.

BACK TO THE ORIGINAL BLOG CONTENT: We were not looking forward to the 2-3 mile back to the trailhead in the blazing sun.

This is not the famous 'Mecca Painted Canyon' but the colored layers on the hillside were amazing in the early morning sun. If you are interested in our hike of 'Painted Canyon and Ladder Canyon', click here to be redirected to that blog.

Specific minerals in the rock layer contribute to their color. Exposure to air and water cause oxidation of the minerals and enhances the color: hematite - red, orange & yellow; manganese - purple and blacks; and clay minerals - green, blue-gray, or white.

Fortunately there were long stretches in the wash with hard compacted sediment so we weren't forced to plod through beach-like sand the entire time.

We found this lonely Mecca Aster growing in the shade of the canyon walls. This flower is native to a limited area of the Chuckwalla National Monument within the Mecca Hills, with a few isolated specimens found in the Indio Hills.

Sheep Hole Oasis is the second oasis on this trail. Although it's reported to be an important source of water for big horn sheep, during our visits in October and April we didn't see any evidence of surface water and the palms did not appear as healthy as in the Hidden Spring Oasis. Could fault movements have redirected groundwater away from this oasis? Only time will reveal the answer.

The few palms in the oasis have clearly been impacted by fire.

Probably the most difficult part of today's hike was locating a route out of the wash and onto the ridge above us.

A long, slow, and steep climb through loose gravel finally brought us to the ridge.

Looking down from the point where we crested, you can see the palms of Sheep Hole Oasis.

We returned to the ridge trail and began the last part of our journey back to the car.

We had no problem locating the car in the parking lot. There's nothing quite like the solitude you find in the Mecca Hills, especially during midweek visits.

Keeping with tradition, we stopped at Shields Date Garden for a date shake to mark the end of another successful day in the Mecca Hills Wilderness.

If you haven't tried one of these drinks then you are missing an epic Coachella Valley treat.