Hiking Willis Palms Oasis: Where the San Andreas Fault Breathes Water
- Steve
- Feb 26
- 15 min read
Updated: Nov 5
Hike Distance: 4.4 miles
Elevation Gain: 531 feet
TrailsNH Hiking Difficulty Calculator: 65 – Moderate
Click here to navigate to the TrailsNH website for a description of the hiking difficulty calculator.
Why Hike the Willis Palms Loop Trail
Hiking the Willis Palms Trail is not about conquering a summit or testing your endurance. It’s about taking the time to look a round and appreciate the environment. It’s about noticing how geology and water come together to create beauty in this unexpected location.
This impressive trail showcases the finest aspects of desert hiking and palm oases:
The multiple options for enjoying the palm oasis experience
The incredible biodiversity on the trail
The complex geology in and around the oasis
The sharp contrast of green against the surrounding brown landscape
The unexpected presence of water in one of the hottest driest deserts
So Many Trail Options
There are several trails that bring you to or through the oasis and all of them start at the same trail head located on Thousand Palms Canyon Road. We have hiked both of the main routes to the Willis Palm Oasis: the Willis Palms Loop Trail and the Willis Palms and West Mesa Trail. Maps for these routes are accessible on AllTrails. The Loop Trail is shown on the left, while the shorter West Mesa Trail is in the center. For most of our hikes here, we follow a modified version, on the right that incorporates the best of both trails. No matter which one you follow you wont be disappointed.
The Indio Hills and Willis Palms Oasis - Whose Fault is This
The 4.4-mile modified lollipop trail that we prefer begins at the base of the Little San Bernardino Mountains within the Coachella Valley Preserve. Nearly everything we observe on this hike results from movement along fault lines. If you've ever walked in the Indio Hills or even just driven past, you've likely noticed how they appear like a narrow wrinkle on the otherwise flat desert landscape of the Coachella Valley. This is clearly demonstrated in this aerial view where the Indio Hills are circled in blue.
These hills are not randomly situated here; they are the visible scars of two powerful fault lines grinding past each other: the Mission Creek fault (MCF) and the Banning fault (BF), which formed because the San Andreas fault splits near the eastern edge of the Indio Hills. See the map below.
Most of the time these faults grind against each other as they move. But here's the twist: in this region of the Indio Hills neither fault runs perfectly straight. They jog slightly to the west to form a restraining bend that causes the two sides of the fault to push against each other. When that happens, the land caught between them doesn’t just slide — it gets pushed upward. The Indio Hills exist because the ground was squeezed up where two faults collide.
According to the California Department of Conservation interactive fault activity map the latitude and longitude for the Willis Palms trailhead (marker circled in blue) places us directly on the Banning Fault which is identified as the South Branch of the San Andreas Fault.
Biodiversity Showcase on a Small Scale
We’re fortunate to live in the Sonoran Desert, which is widely considered to be the most biodiverse desert in North America. It boasts a remarkable array of plant and animal life, including more than 2,000 plant species and 550 animal species. This high biodiversity is attributed to its unique climate, which includes warm winters and summer monsoons, as well as its varied topography, including mountains and canyons, which provide diverse habitats.
The Willis Palm trails showcases the Sonoran biodiversity on a smaller scale which one of its main selling points. Although the trailhead is located in a desert wash environment that doesn’t mean it’s a single habitat. Slight variations in landforms such as ridges, depressions, and mounds, along with differences in water availability and drainage along the fault line, create different growing conditions which in turn favors different plant species and different habitats. As we hike the trail, it will become clear how these factors interact to create a mosaic of habitats.
No sooner had we stepped on the trail when we spotted a coyote wandering in the distance. Normally, coyotes are elusive animals that avoid contact with humans. Most active after dusk and before daylight, they are typically seen only at a distance. While some coyotes may be nomadic or transient and travel over wide areas, others occupy distinct territories that they defend, particularly during breeding and pup rearing. In desert environments where food may be scarce, coyote territories can be greater than 15 square miles. They are omnivores and opportunistic eaters, which means they'll consume what's readily available, including fruits, vegetables, and other plant matter including fruit from fan palms. Coyotes frequently use washes as vital corridors for travel, hunting and seeking refuge from predators and humans.
To start we are surrounded by desert wash habitat. Desert washes or dry streambeds carry water only during and shortly after rainstorms. They are ecological lifelines in the Sonoran Desert. Even though they may be dry most of the year, they provide unique benefits that help sustain desert biodiversity.
Because washes collect and hold more moisture than surrounding slopes, they support relatively ‘lush’ layers of plant life. A great analogy for this plant structure is to think of them in terms of a layered dessert where each plant layer contributes to the overall structure and health of the wash habitat.
The Three Layers of the Desert Wash Habitat
Within the first 0.3 miles we can see plants from each layer of the desert wash habitat and they will continue to be present through the trail.
Canopy: This top layer is formed by the tallest shrubs and small trees that are able to access deeper moisture reserves or temporarily benefit from occasional flooding events. This layer provides some shade and moderates temperature for the plants and animals that reside beneath it; examples include smoke tree and mesquite.
Smoke trees are nearly leafless, with gray-green branches that carry out photosynthesis directly. This minimizes water loss through transpiration while still allowing the plant to produce energy. Like many members of the pea family, smoke trees host nitrogen-fixing bacteria in their root nodules. The bacteria convert air nitrogen into a usable form for plants. This process enriches the soil with nitrogen—a key nutrient for plant growth. This helps plants survive in extremely dry areas like this wash where nitrogen is lacking.
Subcanopy: The middle layer in a desert wash consists of large shrubs that can tolerate the slightly drier conditions without relying on the influence of the canopy; examples include indigo bushes and catclaw.
During one of our hikes, the indigo bushes were in full bloom. They produce small, deep indigo to purple pea flowers in late spring and early summer and occasionally after summer and fall rains. The indigo bush has an intricate gray-green to blueish intricate branch structure similar to a smoke tree. But there are some key differences if you look carefully.
Indigo: medium shrub, usually 3-6 feet tall; slender and flexible branches that feel soft like a tree shrub; blooms late winter to spring; deep indigo-purple flowers clustered along the stems that gives the plant a dusted purple look.
Smoketree: medium to large tree up to 20 feet tall; rigid spiny branches; usually blooms after late spring flashfloods; bright purple to violet pea flowers clustered at the branch tips.
During extended dry periods, indigo can halt growth and photosynthesis almost completely, resuming quickly after rains. This allows the indigo bush to survive years between significant rain events.
Interestingly, indigo is found in a limited geographic area, with its presence in the United States restricted to small regions in California, Arizona, and Baja California in northwest Mexico. Nonetheless, in the Sonoran Desert, where it is present, indigo is relatively abundant and can be seen along most hiking trails. The dark green area on the map illustrates where indigo can be found.
Groundcover: This layer of low-growing shrubs stabilize the soil, provide food for small animals, and contribute to the nutrient cycle; examples include cheesebush and wand holdback
Cheesebush, one of the most common shrubs found in desert washes, has adapted to thrive on the bare, unstable ground here. It is a prolific seeder. These lightweight seeds are easily spread by wind and water. The washes function like conveyor belts, transporting seeds downstream where they settle in sandy deposits. The seeds germinate quickly following even brief rains. Young plants grow quickly compared to other desert shrubs, providing them with a competitive edge in environments where resources and nutrients are scarce.
There is a reason why cheesebush seems to green up almost immediately after a rain event. They carry dormant buds on their stems and root crown. When it rains, these buds can break dormancy almost immediately. In addition, the plant stores starches and carbohydrates in their roots and woody tissue which act like a battery. As soon as water is available, it can instantly fuel new leaf and shoot growth, resulting in significant new development on the plant. Here is a closeup of this burst of growth commonly seen on cheesebush.
With all of this plant growth, the wash offers a mix of shade, food and shelter for a variety of reptiles, including this desert iguana. They are one of the most heat-tolerant reptiles and can remain active in temperatures up to 115°F when other lizards seek shelter. This ability allows them to remain active during the hottest part of the day, potentially giving them an advantage over predators.
Desert iguanas are medium-sized reptiles with a blunt head and a long tail, growing to a total length of up to 16 inches. They heavily rely on the creosote bush for nourishment and protection, frequently digging burrows under its roots. Primarily herbivorous, these iguanas feed on leaves, buds, flowers, and sometimes insects.
Why All Do All These Plants Suddenly Appear
Virtually all traces of the ‘giant crack in the ground’ that people imagine when we talk about the San Andreas fault has been erased. Over hundreds of thousands of years, erosion has obscured any visible sign of the Banning fault but indirect evidence of the fault is found along the trail.
Sudden appearance of more dense vegetation. Notably, the vegetation and plant coverage at the base of the hills is significantly greater that in other areas of the wash. This dense vegetation could not possibly be supported by annual rainfall. It’s likely that groundwater seepage along fault lines is supplying extra water to these plants .
Emergence of clusters of mesquite, willows or cottonwoods in an otherwise sparse desert landscape. Several small to moderate size stands of mesquites were growing at the base of the hills. Their persistence in dry landscapes indicates the existence of significant subsurface moisture.
California fan palms oasis as fault markers. The sudden appearance of fan palms on the slopes indicate we on the fault. They grow almost exclusively where fault zones bring groundwater to the surface. This pattern of oases springing up along major fault strands is repeated throughout the Indio Hills:
Thousands Palms - Mission Creek fault
Horseshoe Palms - Mission Creek fault
Hidden Palms - Banning Fault
I’ll share much more information about these water guzzlers later during when we hike into the oasis.
Linear groves of vegetation on the desert floor. Stand anywhere in front of these palms and you can trace a thin straight line of green.
The answer as to why the desert fan palms grow in a straight line is based in structural geology.
Where the Banning fault crosses the wash, it crushes and seals rocks in ways the trap and then redirect groundwater to the surface.
Where groundwater percolates to the surface, the desert fan palms grow.
Since the fault line runs in a straight line, the palm trees also grow in the same manner. The linear vegetation pattern is easily seen in this satellite imagery of the Willis Palms Oasis.,
These four point taken together provide ample evidence that the first half mile of the journey trail follow the trace of the Banning fault. We’ll spend more time talking about the palms later when we will hike directly through the oasis.
After slightly less than a half of a mile the palms thin out and the slope transitions back to the desert slope groundcover: creosote, brittlebush, and isolated cacti.
During several of our hike here various species of wildflowers were putting on a show.
Emory rock daisy and notch-leaf scorpion weed.
Desert annuals are the ultimate gamblers. They compress their entire lives into a single season when they sense the conditions are right to germinate, grow, flower, seed and die, This entire process can take as little as 6-8 weeks under desert conditions.
Bristly langoisia
One of the major drivers for wildflower blooms is winter rains (November-March). Cool temperatures plus steady rain showers from the Pacific allow moisture to soak deep and stay in the soil. These conditions are essential since seeds sense both moisture and temperature which prevents them from sprouting after a 'false' summer shower.
Desert tobacco and desert sand verbena
Ghost flower
A short distance away the dark rocky slopes give way to several smooth golden-yellow mounds. These rounded hills are not dunes but exposed beds of the Imperial Formation dating back to a time when this desert was a shallow sea. These beds were deposited 5-7 million years ago when the warm marine water of Gulf of California extended into present-day Coachella Valley. They are comprised of marine sands, silt, clay, and ocean fossils. Shell fragments and fossils recovered from this area suggest water depths ranged from 16 to 90 feet.
These beds are exposed because of the tilting and uplift caused by the Mission Creek and Banning faults, but what we observe is merely the eroded edge of a marine layer that is estimated to be 5,000 to 6,500 feet thick in some areas. While it is exposed at the surface in Willis Palms, the Imperial Formation is generally found at depths ranging from 0.6 to 2.0 miles below the surface.
The golden-yellow hue of the Imperial Formation is due to small grains of iron-bearing minerals mixed with marine sediments. Over time, the desert air, rain, and groundwater transformed the iron into iron oxides. In wetter climates, this reaction results in deep red rocks, like those in Arizona. However, in the drier and slower weathering conditions of the Coachella Valley, the oxidation remains lighter, resulting in the golden hues seen in this closeup photo.
As a note, Dave was concerned about including these photos since the coloring looked fake, but these untouched photos reflect the coloration right before sunset,
About a mile from the trailhead, the wash begins turning northward. The landscape changes as we begin hiking into the Indio Hills and leave the open desert floor behind us.
Flowering shrubs and wildflowers continue to dot the landscape including this catclaw acacia.
Milkweed, a common, leafy plant often viewed as a pest by agriculturists due to its affinity to spread quickly and its poisonous sap, but it is the only plant that Monarch caterpillars can feed off of and deposit eggs upon In the United States. In the Sonoran Desert, milkweed are common species found in desert washes. They readily adapt to the sandy soil and thrive in arid and drought-prone conditions
I managed to capture this photo of a Queen caterpillar on a flowering milkweed.
The wash was full of plant life taking advantage of rain water runoff from the hills…
... including this Arizona lupine.
Signs of tilting and uplift along the San Andreas Fault (blue line) are evident in the eroded hills in the wash.
Finding juvenile brittlebush in the wash is always a positive indication but the next few years will be key to its survival. Juvenile brittlebush are highly susceptible to death in their first years primarily due to their underdeveloped root systems and their vulnerability to drought, extreme temperatures, and competition.
After a mile in this wash, we begin a short climb out of the wash on a trail section built into the hillside.
After reaching the crest, we had an excellent view of the path we had taken through the wash and the Santa Rosa Mountains in the distance.
Now, it's a march for the next mile on this mesa, which stands about 100 feet above the wash.
We are entering the second major habitat on the Willis Palms Loop, known as the Creosote Bush Scrub. The soils here are drier, coarser, and more compact. Generally, it is a harsh microclimate with limited water infiltration and minimal organic material, which hinders the germination of new species. The plant community here consist primarily of creosote and brittle bush, the drought specialists. This area exemplifies the classic 'dry desert environment'.
During one of our hikes, while I was taking pictures of a flowering creosote bush, I noticed this desert horned lizard hiding in the shade of the lower branches. These lizards, measuring 3-5 inches in length, have a unique, flattened, toad-like appearance and can be easily recognized by the spines or "horns" on their heads and the fringes of scales along their bodies. Their diet mainly consists of insects, with a strong preference for harvester ants, which can make up to 90 percent of their diet. Desert horned lizards thrive in open, sparsely vegetated areas in the Creosote Bush Scrub habitat of the mesa.
Three of our friends that are always a joy to have on our hikes.
It's easy to see why Creosote Bush Scrub it one of the less diverse desert plant communities. Finding the desert horned lizard earlier on the mesa, serves as a reminder that sometimes you need to work hard to find what thrives in an environment.
After walking a mile, we could see the Willis Palms again. However, this time we were looking down at the cluster of palms.
Getting closer to the palms
A short but steep path leads directly into the oasis. The change is remarkable; you are immediately surrounded by a vibrant green area filled with plants. We have now entered the Riparian/Oasis Habitat, the third habitat we've encountered on the trail.
Of all the sights along the Willis Palms Loop Trail, none are more iconic than the towering California fan palm (Washington filifera) also known as the desert fan palm. How many palms can be seen here? The only known survey of palms groves in the Coachella Valley dates back to 1986. In that survey, Willis Palms ranked as the 4th largest with 612 palms behind three oasis in Indian Canyons: Palm Canyon Oasis - 2511 palms; Andreas Canyon Oasis - 1076; and Murray Canyon - 688. Although it's likely the number of palms have increased in each oasis, there is little reason to believe those rankings have shifted dramatically.
Unlike most desert plants that have adapted to survive in an environment where water is scarce and valuable, desert fan palms disregard water conservation practices. Sporting huge fan shaped green leaves that transpire water vapor back into the air as if they were living in the wet tropics. According to some estimates, these leaves can lose between 25-80 gallons of water per day during the peak summer temperatures.
Young California fan palm sprouts emerging from the sandy damp soil in the oasis.
They lack the structural or physiological adaptations needed for thriving in a hot and dry climate because desert fan palms are confined to rare desert areas where earthquake faults bring groundwater close to the surface. When an oasis develops under these conditions it's referred to as a 'seep oasis'. If you are willing to explore inside the oasis, there is ample of evidence to support this classification. I've seen multiple seeps on our visits to the oasis.
Groundwater in the oases is rich in dissolved minerals, including various salts, from the surrounding rock and soil. The dry, hot desert air causes any water that reaches the surface to evaporate quickly and leave behind the salts which over time accumulates to form the white crust on the surface that we often see in seep oases.
These seeps are essential for the palms' survival. Studies of Washington filifera managed landscapes suggest a mature palm can use 50-130 gallons of water per day during summer months. Without an abundant supply of surface or groundwater, palms perish. Their root systems are relatively shallow, reaching only 8-12 feet deep but they can extend 20-40 outward from the truck. These roots are designed to tap all the water these seep can offer and when it's available they thrive.
The only palm native to the western US, these desert giants can reach heights of 60-75 feet and weigh as much as three tons. According to the US Forest Service, palms can live 80-90 years with some mature specimens living up to 150 years.
Mature palms produce large, hanging clusters of berries, with some stalks weighing up to 20 pounds. The fruit ripens in late summer and early fall, turning from reddish-black to a deep black color. A thin layer of pulp conceals a large seed nearly the same size as the fruit. Fan palm fruits have a slightly dry, chewy texture with a mild molasses and butterscotch taste. During our Friends of the Desert Mountains hikes, we always encourage participants to engage all their senses while on the trail. Naturally, we asked people to taste the ripened palm fruit. Most people picked their own fruit and enjoyed both the taste and experience.
did so and enjoyed the taste.
The California fan palms naturally keep their dead fronds attached, forming a skirt that drapes down the trunk. These skirts serve as habitat and hazards. Birds, insects and lizards find a cool shelter among the dead fronds.
However in a fire, the same skirts can become ladders for flames and fires are all too common in palm oases. Although the fronds are highly combustible, they burn quickly and cleanly, often charring only the outer trunk without killing the crown. If the crown survives, new fronds will emerge within months. These blackened trunks were burned during a fire in 2010.
Here is a picture of the Willis Palms less than 3 months after the fire (courtesy of Desert Stories). While fronds may regrow, fires have a substantial effect on this essential desert habitat. Fires result in immediate fatalities and long-term habitat destruction for animals, particularly those residing and nesting within the skirt. Furthermore, palm seedlings and smaller juveniles can be eliminated, potentially altering the age structure of the groves for many years.
After exploring for a considerable amount of time, a faint path on the edge of the oasis led back to the wash.
As we returned to the trail, we kept observing wildlife. A common side-blotched lizard was soaking up the final rays of sunshine on a rock and ...
... a Swainson's hawk soaring overhead.
This desert cottontail, hiding under some mesquite trees, was likely trying to avoid being seen by the hawk.
Three hours after starting the hike, we were back to the trailhead. Willis Palm Loop was an amazing adventure and I highly recommend this hike to experience a California Palm Oasis.
We stuck afterwards at the trailhead for a beautiful sunset.
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