UCCA VALLEY, Calif. — "Stop! Stop! That one's in bloom!" I cried.

Within a minute, my brother-in-law had pulled the rental car into a rest stop at Joshua Tree National Park, and all four of us tumbled out, adjusting our various cameras — brother Ken and sister-in-law Judy with their sophisticated digitals, my husband stubbornly clinging to his vintage Nikon and me with an any-dummy-can-manage-it Kodak Easy Share. That gorgeous flower, a bright splash of green and yellow framed in fierce golden spines, was surrounded.

Later, we would spend happy hours comparing our shots — not only of that Teddy bear cholla cactus (Opuntia bigelovii) but of this eerie desert world of plants, animals and geological shapes.

Joshua Tree National Park is 800,000 acres of wilderness, campgrounds, four visitors' centers, a preserved homestead ranch, riding and hiking trails, fields of wildflowers in spring and hellish temperatures in summer. It's on Twentynine Palms Highway, a few miles northwest of Palm Springs and 140 miles from Los Angeles.

Here, three related but diverse geo-biologic zones come together: the Colorado Desert on the south and east, the Mojave Desert on the north and the Little San Bernardino Mountains on the west, from which the 4,000-foot peaks overlook a jumble of haunting rock formations and forbidding cacti and yucca trees below.

The park is named for the Joshua tree, so-called by Mormon missionaries, who thought its outstretched arms looked like Joshua reaching out to escort them westward. Yucca brevifolia was the ti leaf of the local Cahuilla people, who used its parts for everything from food to basket-weaving and sandal-making.

Today, the lonely trees dotted around the landscape — they don't cluster but grow upright and alone, and the eldest is believed to be 300 years old — live a protected existence in this intriguing preserve.

JOSHUA TREE NATIONAL PARK OFFERS RARE PLANTS, RUGGED SCENERY AND ADVENTURE

YUCCA VALLEY, Calif. — Driving in through one of the park's three main entrances — Joshua Tree on Park Boulevard; the Oasis a short way east on Twentynine Palms Highway; or Cottonwood off Highway 10 to the south — the first-time visitor to Joshua Tree National Park is hard put to say which is weirdest: the trees themselves or the bizarre rock formations tossed about the flat landscape like slingshot stones left over from a Goliath's smackdown match.

Both woo you to the side of the road where there are frequent pullouts, tempt you into the scrub (despite the occasional side-winder rattlesnakes; just keep your eyes open) and glue your camera viewfinder to your face.

THE TREE OF LIFE

During our first stop, at the Joshua Tree Visitor Center for maps, brochures, and the inevitable postcards and souvenirs, the ranger on duty told another pair of visitors a bit about the Joshua tree and its equally shaggy cousin the Mojave yucca, and I eavesdropped eagerly.

Joshua trees are a weird combination of angular branches reaching skyward, sprouting sharp-edged pompoms of silverly green, their trunks covered with a sort of shaggy dry grass "fur" that conceals the nests of birds and was used by the local Cahuilla Indians to make waterproof shelters and by early settlers for fencing. Its spines aren't all that are spiky; the complex life cycle of this member of the grass and orchid families is equally touchy.

If you see a Joshua tree composed of a single spike, it's a young one, one that's never bloomed, though it may be many years old. Its chances of doing so are, relatively speaking, slim. The flowering of a Joshua tree requires an iffy interaction of sprout growth, weather and assistance from a particular insect. Sprouts, hiding amidst the spikes, may take five or more years to grow. Joshua trees produce their white-green flowers only if both a chill winter and the right amount of spring rain cooperate. The young tree then gets an assist from the yucca moth, which spreads the pollen around. If all goes well, the tree produces a fruiting bunch and, eventually, a new branch.

The Mojave yucca (Yucca schidigera) is a more stunted and long-spined friend of the Joshua tree, often found growing nearby, bearing a crown of seed cones. Park brochures explain that you can tell the difference by looking for frayed edges on the fatter, wider leaves of the Mojave yucca.

In either case, look but don't touch; these plants can slice you.

Like the hardy ranchers, miners, farmers and desert explorers who settled this area, the Joshua tree is a survivor that can regenerate itself after fires and other disasters, sprouting from roots and branches even when the central trunk is killed. It shelters numerous desert animals and insects, and works in symbiosis with others. And it has aided human survival, too. The ranger who gave us our little Joshua tree lecture sounded full of pride in this, yet another example of earth's diversity.

ROCKY SIGHTS

If you didn't know you were in a national wilderness, you'd swear you were on the set of some cheesy 1950s Western, with artfully shaped boulders made of papier mache set just where they ought to be to set off the hero's craggy face or serve as a backdrop for the final shootout.

But the jointed, round-edged and often precariously balanced rockpiles that rise suddenly out of the grasses and dwarf the twisted Joshua trees are real. They are the result of a million years' worth of water wearing away the cracks in solidified blocks of a type of rock called monogranite.

For reasons only a geologist can explain, the monogranite produces an almost mathematical grid of cracks as it cools from magma to rock, splitting both horizontally and vertically. The action of water (and later wind) wears away topsoil above the surface of the water table, rounds sharp edges and pries centuries-slow, patient fingers into the jointing.

Eventually, you have this tumbled landscape, so fantastic that a movie set looks tawdry beside it.

Reach Wanda A. Adams at wadams@honoluluadvertiser.com.