ON THE FAULT LINE PALM SPRINGS JEEP TOUR EXPLORES SAN ANDREAS' SHAKE-AND-BAKE ZONE.

Byline: Story by Eric Noland Travel Editor

PALM SPRINGS - Now this was a true desert mystery. In a parched landscape due east of Palm Springs, the ground all about us was strewn with reddish rocks. But if you looked into the gullies of the Indio Hills, there was nothing but formless gray - not a trace of red.

The puzzle was soon solved for us by Morgan Levine, a guide for Desert Adventures, a jeep eco-tour company that ferries tourists along the geologic oddity that is the San Andreas Fault.

These rocks, it turns out, are taking a ride. Thousands of years ago, they tumbled out of a wash a few miles southeast of here. They've since taken a slow, imperceptible journey on the Pacific Plate, which overlays a sliver of the West Coast and stretches all the way to New Zealand and Japan. The canyon that disgorged the rocks sits on the North American Plate, which extends as far as Iceland.

The two plates are scraping in opposite directions, with overall movement of about 1 to 2 inches a year. Thus, the many clefts in the hills no longer line up with the stream beds that cut them.

In another 10 million years, according to the textbook ``Physical Geology,'' by university professors Brian Skinner and Stephen Porter, those rocks will lie somewhere just west of San Francisco - with the rest of the Los Angeles area.

It's mind-boggling to ponder these forces of nature. It's positively fascinating to examine their evidence up close.

Desert Adventures has been conducting jeep tours for 16 years, but four years ago it added a special enhancement: access to about 1,000 acres of private land that sits smack on the fault. The plot has been family-owned for three generations, and the owners were looking to generate some income to cover costs, so Desert Adventures signed a long-term lease - and received a key to a locked gate.

Beyond that gate, we bounced over a rough dirt road to a palm oasis and learned that it is one of 28 sprouting along the San Andreas Fault in the Coachella Valley. Groundwater crowds the Earth's surface along the fault - and we soon encountered some dirt that was damp to the touch, though rain hadn't fallen here for months.

A subsequent interview with Dr. Sally McGill, a geology professor at California State University, San Bernardino, revealed that scientists have developed two theories in their effort to explain this phenomenon.

``One factor that could cause springs and oases is that the granite on the fault zone is ground up and fractured, which allows water to flow to the surface,'' McGill said. ``The other is that the fault zone can be a barrier to groundwater. The rock is ground up (from the movement of the plates against one another). Water falls upstream, runs into the fault and this impermeable layer of claylike fault gouge, and - instead of continuing to flow underground toward the Salton Sea - comes to the surface.

``I realize those two would seem to contradict each other. We're not sure what causes that.''

In ancient times, the Cahuilla Indians didn't know what caused it, either, they just knew that the area where the trees grew provided the essentials of life - no matter how often or how much the ground shook.

One of the jeep-tour offerings, in fact, is the Indian Cultural Adventure, which explores native life and makes a stop at a restored Cahuilla Village. You'll notice here that the dwellings, or kishes, are essentially huge inverted baskets made of palm fronds. Adobe masonry, a common construction method with other Indians of the Southwest, wouldn't have been particularly practical here in earthquake country.

The village site also has a gravity system of pools built by the Indians to keep water moving.

Another tour option is Lost Legends of the Wild West, which includes a stop at a re-created mining camp.

The peculiarities of the San Andreas Fault are incorporated into both tours, which are offered in the morning and afternoon and can be scheduled for durations of two hours ($59) or three hours ($79). Another offering is a four-hour tour of the fault zone's badlands to the east, including an hourlong hike ($99). Five dollars is knocked off each price for children (age 12 and under) and seniors (age 55 and up).

Desert Adventures claims to place a high priority on training for its guides, and ours certainly knew her stuff. Levine, a desert rat who has lived most of her life in the Coachella Valley, held forth in depth on agriculture, native history, water, windmills and, of course, geology.

She also possessed a playfully dry wit. ``Sign this,'' she told our group of five at the outset, handing over a waiver affixed to a clipboard. ``It says, 'No whining.' It also says I'm the captain. If I say, 'Leave that snake alone,' you will.''

When a tour patron asked how she'd acquired so much knowledge about geology and whether she had a degree in it, she replied, ``I finished the ninth grade and got a library card. If I had a university degree, would I be driving people around in 108 degrees?''

The lack of scholarly jargon, however, is probably a boon to laymen. Concepts are described in simple terms, and clever analogies provide illumination.

The Palm Springs aquifer, for example, should not be thought of as an underground lake, ``as the taxicab drivers here describe it, but more like a bathtub filled up with gravel - and then water part of the way up.''

We were also told of palm beetles ``that look like a cockroach the size of a Chrysler.''

Because of the noise of the jeep, the running commentary was amplified to patrons sitting on bench seats in the back of the vehicle, but I found myself wishing that Levine would get a headset microphone. Before we got to the open country, it was faintly unnerving to bomb along city streets as she held a microphone in her left hand, the gear-shift knob in her right - and steered with her left forearm.

At one point in the backcountry, we pulled to a halt in a dry wash and embarked on a short hike through slot canyons that are conveniently configured in a loop. The sun was blazing, but we were told to leave behind the chilled bottles of water stocked in the jeep's ice chest.

Soon, it was evident why this was wise strategy. The rock walls of these canyons are tortured by seismic activity and flood runoff, and soon the passage was barely shoulder width. In places we had to scramble up, over and down boulders, using our hands to crab along.

In an exploration of one of the canyons, we spotted the nest of a golden eagle. At another juncture, we encountered the tracks of a coyote on a dune. Then the coyote itself.

For many tour customers, however, the high point of the day seemed to be a surface fracture - a spot where the Earth has been literally torn asunder by an earthquake. It's a popular photo op on the tour, and one fellow duly straddled the earthquake crack and smiled for the camera.

In a few million years, archaeologists might have a puzzle to solve when they find that left footprint somewhere just west of Bakersfield.

IF YOU GO

Desert Adventures provides pickup at hotels for its three- and four-hour tours. For its two-hour tours, customers are met at the intersection of Interstate 10 and Washington Street. The jeeps are open-air (though you sit under a canopy), so plan on tasting some dust. You'll be getting out of the jeep in some rough country, much of which is unshaded, so it's a good idea to wear hiking boots or sturdy athletic shoes, a hat and sunglasses. Bottled water is provided. Information: [phone]; www.red-jeep.com.

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(1 -- color) A tour includes a stop in a slot canyon, where a guide points out layers of sedimentation in a rock wall.

(2 -- 3 -- color) Desert Adventures jeep tours of the San Andreas Fault in the Indio Hills include a stop at an oasis, top and above, which forms when water finds its way to the surface on the fault line.

(4 -- 6) Above, Brittany Zobl, 9, with her mom, Sheree, looks at the undigested bones in an ``owl's pellet'' held by Desert Adventures tour guide Jerry Green. Why bones? The birds eat their prey whole. Top, the jeeps take groups on tours of two to four hours in length. At left, Green describes how the San Andreas Fault creates a desert oasis.

Rodrigo Pena/Staff Photographer

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IF YOU GO (see text)