HUMBOLDT REDWOODS STATE PARK, Calif. — Equipped with a laser range-finder, a head for numbers and an explorer's zeal, Michael Taylor has made a sport of finding and sizing up the tallest species on the planet — California's ancient coast redwoods.

"It's a frontier, one of the last frontiers," says Taylor, 40, greeting individual trees like old friends as he scouts a sheltered creek bed where he has found record-setting redwoods in the past. "And it was pretty much unexplored."

In the space of eight weeks last summer, he and fellow amateur naturalist Chris Atkins, 44, discovered what are believed to be the three tallest trees in the world, all of them higher than 370 feet and as much as 2,200 years old. The discoverers christened them Helios, after the Greek sun god; Hyperion, his father; and Icarus, the mythological youth whose waxen wings melted when he flew too close to the sun.

Separately and as a team, Atkins and Taylor are credited with cataloging more extreme trees — those measuring 350 feet and up — than anyone else.

Yet until they located the new champions in Redwood National Park, 90 miles north of here, their achievement was unappreciated outside a tiny fraternity of similarly obsessed scientists and enthusiasts.

Now, after years of tracking trees as a hobby and at their own expense, the men are months away from completing their quest to measure all the loftiest redwoods. They know where California's last unexplored stands are, and by next summer they expect to have canvassed them all. The odds of finding a tree taller than the 379.1-foot Hyperion are less than 1 percent, they say.

Coast redwoods grow in a 470-mile ribbon from southern Oregon to Big Sur, and routinely top 300 feet, or the height of a 30-story building. (The giant sequoia, the redwood's inland cousin, have massive trunks that make them the world's biggest trees by volume.)

Only 36 coast redwoods taller than 360 feet have been recorded. Atkins or Taylor had a hand in locating 28 of them. In the 370-feet-and-up category, there are only four. Atkins and Taylor found them all.

Their stalking grounds are forests where, to the untrained eye, one giant looks pretty much like the next. Yet a prize is as likely to be within sight of a popular trail or highway as hidden in an untouched grove.

A trunk that barely tapers, level ground, proximity to water, a flash of sun-kissed foliage reaching beyond the shaded canopy — these are clues to finding a tree superior to its merely magnificent neighbors.

On a recent afternoon, Taylor spots a contender. Backing up for a better angle, he peers through the range finder. But getting a reading amid a cluster of trunks as wide as mobile homes proves difficult. Taylor lowers his scope and makes his way uphill for another try.

"See how frustrating this can be?" he calls over his shoulder, swatting aside wet ferns and clambering over downed branches. "I can see the top, but I can't hit it."

The men, who also share a passion for Dungeons & Dragons and "The Lord of the Rings," admit that one reason they have emerged as champion tall-tree hunters is that there was little competition.

For more than 30 years, the tallest known redwood was a 367.8-foot specimen that National Geographic Society scientist Paul Zahl found in 1963. Zahl wrote about finding the "Mount Everest of Living Things," and his work gave momentum to an effort to preserve the remaining old growth redwood forests. The terrain he covered became Redwood National Park in 1968.

It was not until Taylor, a kindred spirit named Ron Hildebrant and a botanist named Steve Sillett started compiling a list of tall trees in the 1980s that anyone thought to challenge Zahl's discovery.

It turned out that Tall Tree, as Zahl's find was called, had lost more than nine feet in the years after its discovery, possibly because of weather, disease or the compacting of the soft soil around its trunk by the landmark's many visitors. Sillett remeasured it by climbing to the top and dropping a tape measure to the ground.

For members of the Tall Trees Club, founded by Taylor and Sillett, systematically exploring groves most likely to yield behemoths was made much easier in 1995, when a handheld laser range finder originally developed for the military was marketed to the public.

With a few clicks, the device can calculate an object's height based on readings of the distance to the base and the angle to the top. It accomplishes in seconds what had taken all day using old-fashioned surveying instruments and skill in trigonometry.

The title of world's tallest tree has changed hands — branches? — repeatedly over the past decade, with one discovery after another.

On a morning last August, Atkins and Taylor were still coming off the high of finding 375.3-foot Helios and 371.2-foot Icarus earlier in the summer when they found Hyperion along a tributary of Redwood Creek where they had never been before.

"Ding, ding, ding, we got a winner!" Atkins crowed into his walkie-talkie after the first laser reading.

At times, the pair have been hard-pressed to explain their hobby to friends and family. Taylor, who ekes out a living selling silver on eBay, says that until the discoveries of Helios and Hyperion got media attention, his parents were "horrified" he wanted to rank redwoods instead of make money.

"I was always really fascinated with the extremes — the biggest elephant, the longest anaconda," he says. "Why? I don't know."