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Discover the Thrills of Cave Exploring Along the San Andreas Fault

Updated: Feb 5

INITIAL HIKE: November 2021

UPDATED: April 2022 with Weston & Mackenzie

UPDATED: Jan 2024 entrance to the grotto is no longer possible due to debris flows from the August 2023 tropical storm. I visited the trail prior to offering this hike as a private hike for Friends of the Desert Mountains. I hiked counter clock wise to the 'exit' and could not navigate through all the debris. I've added a few photos to the blog showing how the trail has been altered by storm debris.

After a COVID-related absence of almost 18 months, we finally returned to the Mecca Hills Wilderness. This Wilderness was established in 1994 when the U.S. Congress set aside 26,356 acres in the Mecca Hills to be managed by the U.S. Bureau of Land Management (BLM). This incredible area is located only 35 miles from Palm Desert and is just south of Joshua Tree National Park. Without a doubt, Mecca is our favorite hiking location in Southern California. We usually include a Mecca hike when family or friends visit if they are up for the challenge.

Grotto #1 hike is a double lollipop trail through washes, canyons, and a cave (grotto) created by a combination of plate tectonic and erosion over hundreds of thousands of years. So let's start some cave exploring.

Hike Distance: 8.8 miles

Elevation Gain: 1,125 ft

TrailsNH Hike Difficulty: Moderately Strenuous Score 141. More details concerning the scale are included at the end of this blog.

The empty off-road 'parking lot' was a sign that for this midweek hike we'd be alone when it came time to navigate through the grotto.

Mecca Wilderness sedimentary rocks

The trail initially followed a wash which led to the tops of these hills. The Mecca Hills, situated on the northeast side of the Coachella Valley, came into being as a result of the ongoing collision between the North American Plate and the Pacific Plate along the San Andreas Fault network. Importantly, the San Andreas Fault is not the only fault that has altered the landscape in these hills.

Rolling hills and sandy trails in Mecca Wilderness

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

Hills aligning on southern San Andreas Fault

Once on top of the hills, we followed a ridge line for half a mile. Since the hills have little or no alluvial cover or vegetation, the rocks and their unique structure are dramatically exposed and clearly visible. This unobstructed view of 3-5 million years of tectonic plate destruction is one reason why the Mecca Hills Wilderness has been studied so extensively by geologists and seismologists.

Mecca Wilderness ridge trail into wash

It wasn't long before we had outstanding views of the Salton Sea just above the hilltops. For more information about the iconic Salton Sea, check out check out the blogs about Walking on Volcanic Domes in the Salton Sea and History of the Salton Sea.

Mecca Wilderness ridge trail to the caves

After a while, the trail slowly descended a few hundred feet to the Hidden Springs Canyon Wash. This tortured and twisted environment exposes a 0.75 mile-thick stacked layer of sedimentary rock strata deposited over millions of years. This layer has been repeatedly inverted, uplifted and deformed by movement along the faults in these hills.

Mecca Wilderness wash and folded sedimentary rock hills

Unfortunately, not all the trails today would be as clearly marked or evident as this section heading down to the wash.

Mecca Wilderness eroded trail to wash

Erosion caused by monsoon rains and winds constantly reshape this environment. The remnants of collapsed hills were obvious on both sides of the wash. The difference in 'resistance to erosion' of the various layers creates distinctive features such as the more resistant dark-colored cap on this hill that protects the less resistant tan layers below it.

Mecca Hills sedimentary rock hills and erosion grotto trail

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

Hidden Spring Canyon on grotto trail, palo verde trees

The wash began to narrow and the walls began to creep upwards.

Mecca Hills tall canyons

Weston and Mackenzie took shade under the flowering palo verde tree; it was the last shade area we'd encounter until we reached the grottos. The Spanish translation for 'palo verde' is 'green stick'. It's an appropriate name since all parts of the tree from the leaves to the branches and trunk are green. Unlike most trees, a palo verde can perform photosynthesis through its bark something that in most plants only occurs in leaves. These trees are superbly adapted to the desert and are among the most drought tolerant trees. A funny fact. the seed pods and flowers of the palo verde are edible. We haven't tasted them yet; maybe the next time.

Flowering palo verde tree Mecca Wilderness

After about 1.8 miles we approached a reddish-brown sandstone gate which opened to our left. The opening looked like it was chiseled away, leaving a clear path for adventure seekers.

rock opening to Hidden Springs Oasis Mecca Wilderness

These canyon walls are composed of the 'Palm Springs Formation', a sedimentary rock strata deposited in the Pleistocene Era (2,580,000 to 11,700 years ago). Over time, layers of sediment from erosion of the adjacent mountains as well as runoff from the ancestral Colorado River were buried here one on top of the other. The tremendous weight of each additional layer compressed the layers and squeezed out any water and then chemical processes kicked in to 'cement' the sediments together to form sedimentary rocks layers. In the following photo you can see multiple layers of sedimentary rock strata.

Palm Springs sedimentary rock formations Mecca Hills

Rock-fall debris from the upper layers created a few tight spaces along the trail. These conglomerate sedimentary rocks are comprised of rounded or angular rock fragments that are cemented together. The plant debris at Dave's feet was caused by rushing waters that uproot plants which accumulate at 'choke point' like this tight spaces.

Squeezing through these openings was a challenge not quite cave exploring in the grottos but it was still fun.

Cave exploring Mecca Hills grotto trail

Less than a quarter of a mile after passing through the 'gate' we reached Hidden Spring Oasis. From the looks of these Washingtonia filifera, which are the only native palm tree in California, the oasis is providing sufficient water to maintain this small but healthy 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, they can only grow where abundant water is at or near the surface.

These palms can grow up to 59 ft in height and typically live 80-250 years. The trademark difference, between these palms and other palms commonly found in California, is that when the palm fronds die, they remain attached and drop down to cloak the trunk in a wide skirt. The skirt creates provides safe haven for many small mammals, birds, and desert reptiles including rattlesnakes. Word to the wise - never stick your hand into a palm skirt.

Hidden Springs Oasis Mecca Wilderness, desert fan palms

When we first hiked this trail in October, we observed a small pool of standing water in the palm grove. Groundwater percolates through fracture in rocks and sediment along the Hidden Springs Fault that runs through this area. Even small pools such as this are critical for the survival of animals that live in the Mecca Hills.

Pools of water Hidden Springs Oasis Mecca Hills

A palm seedling only a few inches tall represents a positive sign for a hopeful future. It's been estimated that with sufficient water, germination and survival of seedlings need occur only once a century to maintain a palm oasis. Maybe we'll get an opportunity to check on this 'little guy' over the next few years.

Seedling desert fan palm in Mecca Hills

Several ocotillos were thriving along the fringe of the oasis. These large shrubs with long cane-like spiny stems are more closely related to tea and blueberry bushes than cacti.

Ocotillo with leaves Hidden Springs Oasis Mecca Wilderness

Small bright green 1-2 inch leaves grow from the thorny stems when there is enough moisture.

Leaves on ocotillo Mecca Hills

Although the trail disappeared after the oasis, we knew the trail continued on top of this ridge.

Eroded trailto the ridge from Hidden Springs Oasis

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

Climbing out of Hidden Springs Oasis eroded trail

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.

Grotto trail ridge looking down in Hidden Springs Oasis

Initially the trail clung to one side of a canyon wall to our left. Significant erosion in several areas caused slow-going.

Mecca Grotto Hills ridge trail

After a while, the trail swung eastward to a series of rolling hills. It resembled a moon-scape; it was barren, rocky with no one in sight.

Mecca Hills Grotto trail

Our next waypoint, Hidden Spring Canyon, appeared to our right. Dave began scouting for a path into the canyon. The closer we got to the canyon, the less defined the trail became until it finally disappeared in the rock and rubble.

Mecca Grotto Trail

After hiking for more than 3 miles, Dave found the 'best gully' and we descended into the canyon. Fortunately, the path wasn't quite as difficult as the photo portrays.

Mecca Hills Grotto trail heading into wash

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.

Narrow wash leading to mecca Hills Grottos

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

Slot canyon leading to Mecca Hills Grotto trail

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

Mecca Hills canyon rock debris

By now the canyon walls were towering over us. This incredible landscape and fascinating geology are what drives us to hike and explore the Mecca Hills. There are not many places in Southern California that offer this combination of 'fun' factors.

Mecca Hills grotto trail and cave exploring

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 million years ago that slowly eroded this canyon, cutting deeper and deeper without expanding the area between the walls.

Mecca Hills grotto trail and cave exploring

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.'

Mecca Hills cave exploring grotto trail

Look at how the right-side of this rock debris is almost straight. At some point in time, it cleaved perfectly from the canyon side-wall, fell to the floor but somehow managed to remain intact as a single rock formation.

Mecca Hills grotto trail rock debris

More fun squeezing through tight spaces. We were lucky and could squeeze through without taking off our packs. During other hikes, we haven't been as lucky.

The angular clasts or rock fragments embedded in the conglomerate indicate they were formed close-by since rounded clasts are generally the product of long distance transportation. These conglomerates resemble poorly mixed concrete and the large clasts made great hand and footholds.

Squeezing between rock leading to Mecca Hills grotto caves

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 fast moving water transported and deposited large clasts but as the flow velocity decreased only smaller clasts and then just sediments remained to be deposited. This process was repeated over and over again building a new layer each time.

Squeezing between rocks leading to Mecca Hills grotto caves

After hiking almost 4 miles, we reached the grotto (opening, bottom left of center) and began our cave exploring adventure

Mecca Hills grotto cave opening

We donned out headlamps and entered the darkness. Entering on level ground for the first few feet made it easier to adjust to the low-light conditions.

Entering Mecca Hills grotto cave exploring

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

Climbing through Mecca Hills grotto caves

Dave snapped this photo as I maneuvered using the 'stepping stones' to avoid having to squeeze through the narrow opening at ground level.

Mecca Hills grotto cave exploring with headlights

Can you imagine being in Hidden Spring Canyon or worse yet these caves when monsoon rains or thunderstorms move across the area? Although 'surprise' rain events are not common in Mecca, we always check the weather forecast when we're hiking in the Hills. If we get conflicting information then we go straight to the National Weather Service site. There are a number of excellent site that provide information about the hazards of hiking in slot canyons - check them out before you go.

headlight in Mecca Hills grotto cave exploring

We needed to do some crawling to exit the grotto through this opening. However our cave exploring was far from over.

Tunnel exiting Mecca Hills grotto caves

Here is a photo looking up at the ceiling at we exited the grotto. Huge rocks the size of houses were wedged between the walls. I've included a photo taken from outside which better displays 'unusual' positioning of these rocks.

Ceiling of Mecca Hills groto cave exit

The end in sight.

Narrow exit of Mecca Hills grotto cave exploring

The faces of happy hikers. Weston and Mackenzie are always up for a challenging hike and we still had more ground to cover.

Hikers exitign Mecca Hills grotto cave exploring

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.

Mecca Hills grotto cave exit

Photo from 1996.

Mecca Hills grotto cave exit 1998 photo

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

Cave exploring in grotto Mecca Hills

There were narrow openings overhead so there was no need for headlamps.

Crawling through opening in Mecca Hills caves

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

Squeezing through small space in Mecca hills grotto caves

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

Squeezing through small exits in Mecca hills grotto caves
Climbing out of Mecca Hills grotto caves

Two small ladders were the last obstacle we faced.

Using ladder to exit the Mecca Hills grotto cave trail
Using ladder to exit Mecca Hills grotto cave trail

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

Climbing out of Mecca Hills grotto caves

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 downthey 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.

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

Walking through Hidden Springs Canyon Mecca Hills

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

Mecac Hills grotto trail multicolored hills

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.

Hikign in Hidden Springs Canyon wash Mecca Hills grotto trail

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. Has movement along the faults caused groundwater to be diverted away from this oasis? Time will tell.

Mecac Hills grotto trail to Sheep Hole Oasis

Probably the most challenging part of today's hike was finding a path out of the wash and on to the ridge above us.

Climbing out of Sheep Hole Oasis to Ridge Mecca Hills grotto trail

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

Steep trail from Sheeps Hole Oasis to Mecca Hills ridge trail

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

Sheep Hole Oasis Mecca Hills

We were back on the ridge trail and started the final stretch back to our car.

Mecca Hills ridge trail to grotto

We had no problem finding the car in the parking lot. The is nothing like the solitude you experience in the Mecca Hills - at least during midweek trips.

Mecca Hills Grotto trail parking lot and trailhead

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.

Shield date shake

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

Drinking Shields date shake after hiking

TrailsNH Hiking Difficulty Calculator For Mecca Grotto #1

The TrailsNH Hiking Difficulty Calculator provides you a better sense of the challenge a hike may require. The goal for this calculator is to help you determine how doable a hike is for you.

TrailsNH extended the established 'Shenandoah Hiking Difficulty Scale' from 250 to 500 and added two new effort categories: 'Challenging' and 'Bomber' hikes.

They also include assessments for Energy Miles and Steepness Rating, Grade, and Angle which they believe provides an overall better evaluation of hiking demands. Click on the link to navigate to for more detail, including the formulas they use for each assessment.

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