Towering windmills, whirring in unison and dominating the landscape along the San Gorgonio Pass, mark the entry into Riverside County's Coachella Valley, home of Palm Springs and a host of other well-known desert resort cities.

Awed by the immensity and mesmerized by the whooshing of the hulking electrical generators, I had no inkling that I was getting my first glimpse of the geologic results of the San Andreas Fault.

This wind tunnel, created by San Gorgonio Mountain to the north and Mount San Jacinto to the south, is the first visible artifact of the San Andreas Fault, and it produces one of the windiest place on Earth.

The fault -- more correctly a system of faults -- is responsible for most of the more dramatic natural features of the region.

My husband and I planned a two-day hike into the Mecca Hills in the eastern Coachella Valley between Indio and the Salton Sea.

I never expected to fall totally under the spell of the San Andreas Fault and the colorful landscape its grinding and heaving have created.

Our group of hikers met at the entrance to Painted Canyon Road, a 4-mile washboard dirt road intersecting state Route 195 about a mile east of Mecca. Dr. Monte Marshall, a professor of geology at San Diego State University, proved to be an expert guide.

"The canyon is world-renowned to geologists and especially to geology professors," but little known to casual tourists because of its location off the beaten track, Marshall said. "It's one of the best places in the world to see the effects of seismic activity so clearly."

For 10 hours over two days, Marshall led us along multihued cliffs and through the high-walled box canyon, pointing out rocks that range from lavender and rose through brick, sage, chocolate, zebra stripes, and even the traditional gray and buff. The colors, the result of molten elements that colored the rock at its formation, gave the canyon its name.

Marshall showed us ancient rocks of widely varied ages and mineral composition that had been compressed, bent, twisted, sliced, fractured and turned sideways by the Earth's heaving.

He explained that the San Andreas Fault is a break in the Earth's crust where the Pacific and the North American plates grind against and slip past each other, producing earthquakes and distinct changes to the landscape. It's not a single fault but a system of faults starting off the Pacific coast of Cape Mendocino north of San Francisco and running about 700 miles south to the United States/Mexico border.

Marshall said that the best way to see the San Andreas Fault is from the air. "You have to keep going back and forth between the different scales to put the puzzle together. You need to go out and pound the rocks and see how they're deformed and then go up on a hill and see the whole thing."

But, without the benefit of a knowledgeable geologist as a guide, how could a curious hiker have such an experience? Internet searches produced a number of first-hand accounts, many with detailed hiking and trail instructions, maps, and colorful photographs.

"You really need someone to show it to you and explain it the first time," Marshall said.

Enter the commercial tour operator. Mary Dungans founded Desert Adventures in 1988. Based in the Palm Springs area, her firm offers tours on the San Andreas Fault and other desert attractions. "My tours are based on educational fun, and are aimed primarily at the corporate market," although she also hosts tourists.

"Doctor Doug" Thomson, self-described "Faultmeister of Palm Springs," started his San Andreas Fault Tour three years ago, after living more than a decade in the desert.

Doctor Doug's tours use a 24-passenger executive coach. They start at the San Gorgonio Pass amid the windmill farms, crisscross the San Andreas Fault, and end up at the Thousand Palms Oasis.

The oasis is a remarkably peaceful spot to end a tour of San Andreas Fault. With solitude broken only by the singing of birds and whisper of palm fronds, it's a great way to experience a vestige of the old Palm Springs.

Nicole Sours Larson is a San Diego writer.

If you go

San Andreas Fault

GETTING THERE: To go to the Painted Canyon from Palm Springs, take I-10 east through Indio to state Route 195 (Box Canyon Road). Go southwest on state Route 195 to Painted Canyon Road, a dirt road accessible to two-wheel drive vehicles. The canyon and fault zone begin about 2 1/2 miles along the road, which ends after about 4 miles, where it is blocked by boulders. The main portion of the canyon begins there.

WARNINGS: Summer temperatures reach 110-120 degrees. At all times, monitor the weather forecast for rain, which can produce dangerous flash floods.

TOUR OPERATORS: Desert Adventures Jeep Eco tours, 67-555 E. Palm Canyon Drive, Cathedral City, (760)-324-JEEP or 888-440-JEEP; www.red-jeep.com. Tours range from $59 for two hours to $99 per person for four hours.

Doctor Doug's San Andreas Fault Tours, 1775 E. Palm Canyon Drive, Palm Springs, (760) 322-6029; www.sanandreastour.com. Tours 3 1/2 hours long cost $65 per person.

INFORMATION: Thousand Palms Oasis, Thousand Palms, (760) 343-1234.