When I was a kid, I sometimes wished that my family went on normal vacations.

Normal was what my elementary and middle-school classmates did over spring and summer break, flying to wave-kissed beaches or hitting flashy amusement parks. Not my family: My parents would load my two half-sisters, my brother and me into a big blue Dodge van with finicky air-conditioning and drive us hundreds of sweaty miles to exciting destinations like Lusk and New Castle, Wyo., Broadus and Miles City, Mont.

Amusement parks, as far as they were concerned, held nothing but crowds, noise and cheap gewgaws, and Mom, whose fair skin burned easily, was not fond of prancing about in a bathing suit. But the broad and sparsely populated reaches of eastern Wyoming and Montana offered clear, dry air, sweeping skies, and an intoxicating sense of freedom. Best of all, their badlands and breaks were scattered with the remains of the late Cretaceous -- mineralized seashells that in life, 100 to 65 million years ago, cradled tentacled creatures in the dark of an inland sea.

Decked out in long-sleeved shirts and pants, broad-brimmed cloth hats and boxy over-the-spectacles sunglasses, Mom and Dad led us across this dry country, teaching us the difference between placenticeras and scaphites, baculites and didymoceras.

To sweeten the deal, they booked rooms in motels with swimming pools, and when we were older, allowed us to bring friends who were curious (or brave) enough to join us in the baking expanses. Even so, we kids stopped going in late high school, more thrilled by the prospect of a parent-free house. With barter and bribe no longer necessary, Mom and Dad could finally pursue their obsession untroubled by our demands for normalcy.

So when, at 31, I ask whether I might tag along on a weeklong fossil trip near Casper, Dad pauses.

"How long do you think you'll join us for?" he asks.

"A day or two?" I suggest.

"Oh, good," he says. "We wouldn't want you to cramp our style."

My folks are not the sort of people you'd expect to find mutual passion in the dusty shales and back-road towns of the rural West. When they joined the local gem and mineral club in the early '80s, it was to encourage my older sister's interest in rocks. They had other scientific pursuits: Mom, in her late 30s with fluffy brown hair and a ready laugh, was a meteorologist; Dad, in his early 40s with a black beard going salty, was a solar physicist.

Dad never planned to settle beyond the 100th meridian. "I cannot claim that I was eager to be in the wild outdoors," he says now. The youngest of four, he grew up in a tiny Connecticut town and followed his brothers, father and uncle to Harvard, then got a Ph.D. at MIT. He would have stayed on there, but a teaching job unexpectedly came up at University of Colorado-Boulder, and he and his first wife moved to the foot of the Rockies. Even then, he stayed connected to the East, vacationing at the seashore or visiting family. It wasn't until that marriage ended and he married Mom -- they met at Boulder's National Center for Atmospheric Research, where they both still work -- that he began to learn more deeply about the place he had landed.

Mom was also a transplant. She grew up in Columbia, Mo., a tomboy among three brothers, two of whom were wild, high school football stars. Their house fronted lush woods where she picked Cheerio-shaped stones -- which she later learned were fossilized segments of sea-lily stalks -- from cliff and creekbed. At first, she wanted to be a firefighter, an unusual ambition for an 8-year-old girl in the '50s. Then lightning struck, exploding the house's chimney and part of its roof, and turned her interests skyward.

It was the topography that drew her West. "When I was a little kid, I always fantasized about climbing in the mountains," she says. So she headed to the University of Washington in Seattle for her own Ph.D. -- and for mountaineering in the Cascade and Olympic ranges -- and then to Boulder for her post-doc.