Fossil Hunting in the Yuha Basin
by Lynn Bremner
In April, when the Sonoran Desert is hot, but not scorching, we took a day trip to the Yuha Basin in search of ancient fossils. The Yuha Basin lies in Imperial County on both sides of Interstate 8, approximately 100 miles east of San Diego, California. It can be accessed at the Dunaway Road Exit, which is also called the Dunaway Staging Area for Limited Use Off-Highway Vehicle (OHV) Recreation, about 10 miles west of El Centro, California.
By the time we arrived at the Dunaway Road exit at 10:00 am, the temperature had already reached 98 degrees. Dunaway Road is only paved for a few hundred yards on the south side of the freeway before it ends at the main entrance to the Yuha Basin.
Equipped with a Gem Trail Guide, several area maps and a iPad preloaded with TOPO maps, we were ready to begin our journey into the Yuha Basin. Our destination was the Shell Beds, where 6 million-year-old oyster shell fossils and concretions can be found.
One of the trails
The Gem Trail Guide map shows a series of dirt roads with mile markers and washes as landmarks. Since there were a number of dirt roads leading from the end of Dunaway Road, it wasn't clear which one we should take. After analyzing the Gem Trail Map, we decided to take the road to the right which headed southwest.
According to the map, we needed to travel 1.6 miles before we would turn left on another road. We had only traveled about .5 mile when our road seemed to disappear into a maze of trails (New Rules). Totally confused, we decided it was time to pull out the iPad and its GPS system to find out where we were and which direction we needed to go to reach the shell beds.
With the GPS on, the screen displayed a TOPO map of the Yuha Basin with an arrow pointing to our exact location (within 100 feet). The maps are very detailed and contained the location of the shell beds as well. (32.732781, -115.836939)
Within 30 minutes, we reached the edge of the shell beds and parked in a dry wash to explore the area. As I looked out the window, I spotted a desert iguana basking in the sun next to an oyster shell fossil. I quickly grabbed our video camera and captured some footage of the iguana before it scurried off into the nearby brush.
As we began to explore the area, I noticed the ground of the dry wash was littered with oyster shell fossils. The walls of the wash were formed in layers, and I could clearly see where the shells once covered the basin floor. The oyster shell fossils are remnants of Lake Leconte, which covered most of Imperial and central Riverside counties about 6 million years ago.
We collected a few samples of oyster shell fossils and some rocks with shells embedded in them. As I scanned the area, I found an interesting white- colored crystal specimen in the sandy wash. Later, I was able to identify the sample as a selenite crystal, which can be found in the soft sand and soil areas of the Yuha Basin. These crystals are fragile and need to be handled carefully.
If you are an avid rockhounder, you can search the area for gypsum, which is commonly found in the shell bed area. Agate jasper and obsidian can also be found closer to the Dunaway Road Exit, approximately 2.5 miles southwest of the basin entrance.
It's hard to believe the bleached desert flats of the Yuha Basin were once covered with lush vegetation, vast lakes and numerous Indian encampments. The fossils, geoglyphs, and other evidence left behind are the only clues we have to tell a story that spans millions of years.
Today, the Yuha Basin is home to many animal and plant species which have adapted to its harsh environment. The BLM has designated 40,622 acres of the Yuha Basin as an Area of Critical Environmental Concern (ACEC). The purpose of the ACEC is to protect sensitive natural and cultural resources while providing for a wide range of uses.
After leaving the shell beds, we continued our exploration of the Yuha Basin, heading northwest. We slowly worked our way through the maze of trails as we searched for a more direct path to Route 98, which would take us back to Interstate 8 and the small town of Ocotillo.
In our travels we came upon a fenced-in area that looked like some sort of landmark. As we approached the fence, we spotted a sign that told us the site was the Yuha Geoglyph, which was constructed by prehistoric Native Americans. A geoglyph is a large symbol etched into the ground by clearing lines in the surface layer of small, dark rocks (known as desert pavement) to expose the lighter soil underneath.
Since we were level with the site, we were unable to appreciate the geoglyph images, but the landmark did show an aerial view of the geoglyph. In 1975, the geoglyph was damaged by vandals and has since been reconstructed by the Imperial Valley College Barker Museum and BLM.
Not far from the Yuha Geoglyph is another historic landmark, the Yuha Well. Although we didn't get a chance to visit the well, the BLM offers an Access Guide that provides the following information.
Led by Indian guides, Captain Juan Bautista De Anza was the first Spanish explorer to visit the Yuha Basin. Some 200 years ago, his party replenished their water supplies here before pushing on in their quest to establish a trade route between Arizona and the Pacific Coast. Yuha Well became an important oasis for later travelers and settlers who followed the Anza Trail through this harsh land.
Notes: While driving the numerous trails and roads in the Yuha Basin, you will see various numbered markers throughout the area. These markers are maintained by the BLM and correspond to a route map called the "Imperial Valley South Desert Access Guide #22." (Click to see map.) The BLM produces a series of Access Guides for most of the areas it manages. The BLM is in the process of revising and updating all of their Access Guides. The Access Guides can be purchased from the BLM or related ranger stations.
Related Books & Gifts - Trading Post
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BLM California Desert OHV Areas
Yuha Desert OHV Area
Minerals & Geology Index
Places to Go in California
Outdoor Recreation: Auto Touring & Off-Roading
Outdoor Recreation: Rock Hounding & Treasure Hunting
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