BACK ROAD ADVENTURE Organ Pipe Cactus National Monument

adventure Loop Drive Discloses the RICH DIVERSITY of ORGAN PIPE CACTUS National Monument

THE MEANDERING 53-MILE, WASHBOARD- rutted Puerto Blanco Drive loops through the heart of Organ Pipe Cactus National Monument. Like the tenacious, understated extravagance of the Sonoran Desert, it lulls you with the long sweep to the horizon-but it harbors surprises. A flood in August, an elf owl in a saguaro and an egret amid cacti rate among the treasures hidden in the silent, sun-drenched desert that stretches to the horizon on both sides of the road. Then, just when you've absorbed all the scenery, the day ends, the sun sinks, the shadows lengthen, the colors glow and you stand amazed in the shimmer of silence.

Turn off State Route 85 into the Organ Pipe Cactus National Monument visitors center, 5 miles north of the border town of Lukeville and 34 miles south of the mining town of Ajo. The center provides the perfect staging ground for an exploration of one of the most varied and interesting deserts in the world, which, at 1,800 feet in elevation, is graced by both winter rains and summer monsoons. You can pay your monument entrance fee and browse the exhibits and bookstore to plan your adventure.

Most people hurry on down the asphalt-missing everything. Many opt for the beautiful-but-busy two-hour, 23mile, bumpy dirt Ajo Mountain Drive to the east. On the other hand, the dusty, half-day (or longer) Puerto Blanco Drive to the west offers solitude and a heady taste of the desert suitable for most passenger cars if you drive carefully and bounce cheerfully.

The road winds, climbs, dips and bumps through a jagged, volcanic desert with a surprisingly complex ecology and unexpectedly rich human history. Note that the northern half of the road is two-way traffic for only the first 5 miles. A portion of the remaining road is one-way, so if you continue, you're committed to the whole 53-mile journey.

About 12 miles in, the road climbs a long, sloping pile of sediment washed out of the Puerto Blanco Mountains, a stretch that offers some of the Southwest's most spectacular wildflower displays after a wet winter. The road climbs up to a low pass harboring one of the drive's most rugged, cactus-rich and scenic stretches. At the picnic area nearby, you can ponder the vivid and violent geology. Starting 110 million years ago, the landscape was forged in a series of cataclysms caused by the bumping and grinding of gigantic crustal plates. The 3,000-foot-high Puerto Blanco Mountains are made of 18-million-year-old rhyolite, which is molten granite spewed out and cooled at the surface instead of deep in the Earth. That jagged, unsoftened volcanic history has created an uncompromising landscape, with starkly tormented ridgelines, ripped-open canyons and long, rocky slopes. Go another 12 miles and you come to a fork, where you hit a two-way stretch of road back to the highway. An unmaintained jeep trail veers off north toward the Bates Mountains and seldom-visited points both north and east. To finish the Puerto Blanco Drive, keep going south. After 2 miles, you'll come to a short spur road leading to Quitobaquito Springs, the most

TRAVEL ADVISORY: Public access to the roads along the international border is sometimes restricted, and travelers should check at the visitors center for current conditions and accessibility.

WARNING: Back road travel can be hazardous if you are not prepared for the unexpected. Whether traveling in the desert or in the high country, be aware of weather and road conditions. Make sure you and your vehicle are in top shape and you have plenty of water. Don't travel alone, and let someone at home know where you're going and when you plan to return. Odometer readings in the story may vary by vehicle. ADDITIONAL INFORMATION: Organ Pipe Cactus National Monument, (520) 387-6849.

[LEFT] Reflected on the surface of Quitobaquito Springs, the curved trunk and lush green leaves of a cottonwood tree contrast with its desert surroundings. JACK DYKINGA [BELOW] Fuchsia Parry's penstemon blooms trumpet their presence beside the remains of a tree cholla north of the Puerto Blanco Mountains.

RANDY PRENTICE Commonly called “old man,” senita cacti may bloom from April through August. JACK DYKINGA A surprising and absorbing stop on the route. Here, a 30-gallon-a-minute spring gushes 2,000-year-old rainwater, which runs down a grassy wisp of a stream into a pond. Forced to the surface by a fault that has created an underground dam of crushed rock, the miraculous spring has nourished human beings for millennia. It has undoubtedly saved thousands of lives, especially during the California Gold Rush when it provided one of the few reliable water sources on the aptly named “Devil's Highway” between Tucson and Yuma.

The Tohono O'odham call it A'al Waipia, “little wells.” They farmed it until the government bought them out in 1938 and destroyed one of the oldest human settlements in North America. Now the pond harbors endangered pupfish-remarkable Ice Age survivors that can tolerate hot, salty, lowoxygen water, but not the groundwater pumping and the voracious introduced fish that have degraded the streams, ponds and seeps where pupfish used to live.

The spring has played a vital role in the myths and survival of people stretching back at least 12,000 years, the age of finely shaped spearpoints left by long-vanished mammoth hunters. Although scientists have surveyed less than 3 percent of the monument, they've located more than 400 archaeological sites.

When the first Europeans arrived, they found the peaceful and deeply spiritual Tohono O'odham living here, nurtured by a rich culture exquisitely adapted to surviving in a land where years can pass between rains. The Tohono O'odham farmed the deep desert, relied on scattered springs and tanks and regarded the world with reverence and wonder.

The oasis offers a soothing and historic stopping point and a marvelous birding spot, where startled vermillion flycatchers flit through the mesquite and incongruous herons and egrets pick through the bulrushes. However, a rash of thefts in the parking area 100 yards from the thicket of trees and bulrushes surrounding the pond make it risky to leave your car untended.

Returning to the Puerto Blanco Drive, you can continue east along the Mexican border. About 9 miles from the spring, a spur road leads north for 5 miles into the aptly named Senita Basin, perhaps the prettiest place on the whole route.

The smoothed and sculpted Sonoyta Mountains are made of pinkish granite, which cooled deep beneath the surface instead of frothing upward like the rhyolite Puerto Blancos. The sunny exposures and cold-airshedding slopes nurture a surreal wealth of cacti, not to mention the bizarre elephant tree. A single elephant tree, which thrives in Sonora, Mexico, perches on a hillside overlooking the road. Squat and thick, the bulbous, odd limbs of the elephant tree have strange leaves and waxy, skinlike folds of bark.

The organ pipe and senita cacti that dominate the basin seem no less aesthetic and dramatic. The linear saguaros jostle with the orange-spined, pleated organ pipe cacti and the smooth, gray-bearded senita. More frost-sensitive than the stately saguaro, organ pipe and senita occur together nowhere else in the United States. They have evolved all sorts of adaptations to heat and thirst. For example, their specialized metabolism allows them to absorb the sun's energy during the day but hold their breaths until nightfall when they can open their pores and finish photosynthesis with minimal water loss. They have transformed the leaves they wore in the tropics-where they originated-into needles, which block up to 80 percent of the sun at their delicate growing tips, protect them from hungry nibblers and even insulate them against rare snows. When you reach the Senita Basin, you can lean up against a skin-smooth slab of pink granite in the lengthening shadow of a gray-bearded cactus and do nothing at all while the planet spins, the sun subsides and the light saturates the desert-transforming brown to orange and rust to red.

And then, if you sit very still, you'll hear the shimmer of secrets in the Sonoran silence. AH