The Burgess Shale, a fossil bed high up in the Rockies in Canada's Yoho National Park, is rich with creatures so fantastically bizarre and exquisitely preserved that they have transformed science's understanding of early life on Earth.

We were going 2,500 feet up — and 500 million years back in time. A little freezing rain wasn’t going to stop us.

Tucked into a Rockies mountainside 6,700 feet above sea level at British Columbia’s eastern edge lies the Burgess Shale, a fossil bed rich with creatures so fantastically bizarre and exquisitely preserved that they transformed science’s understanding of early life on Earth.

Naturalist and author Stephen Jay Gould devoted a 1989 book to the find and the scientific controversies it generated. “Without hesitation or ambiguity,” he wrote, they are “the world’s most important animal fossils.”

The 1909 discovery laid bare the so-called Cambrian Explosion — a sudden blossoming, a half-billion years ago, of numerous new life-forms, including many with unfamiliar body shapes and odd appendages.

Save 75% on a Digital Subscription Today

One wormlike creature found there is now considered the ancestor of all later vertebrates, or animals with spines. But many others, like the inch-long Hallucigenia — a science-fiction nightmare with twin rows of spikes on one side and a double row of tendrils on the other — are best described as the Smithsonian Institution does it: “Weird wonders with no obvious relationship to any other living or extinct group.”

Visits by hikers to the Burgess Shale, which lies within Yoho National Park in B.C., are restricted to small authorized groups with guides, although it’s no longer an active exploration site. Electronic devices detect unauthorized intruders.

Our trek began near the B.C. hamlet of Field, at one of Canada’s highest waterfalls, the 833-foot Takakkaw Falls.

Steven, our friendly graduate-student guide from the Burgess Shale Geoscience Foundation, led us up the fairly steep 6-mile trail. We stopped for occasional trailside lectures about fossils, glaciers, lichen and pretty much anything else under the sun.

Steven explained that the Burgess fossils were likely created when mudslides swept the Cambrian critters off the edge of an underwater continental shelf and instantly buried them in deep, oxygen-less waters. That preserved details usually not found in fossils — a creature’s soft tissues, even what it had swallowed just before its untimely demise.

One thing he didn’t tell us was that the site’s discoverer, Charles Walcott, head of the Smithsonian Institution, totally misinterpreted the fossils and didn’t grasp that some belonged to evolutionary dead ends with no living counterparts.

We climbed to the edge of the quarry, where visitors must leave all backpacks and hiking sticks to prevent pilfering of fossils or damage to the site. Our guide handed out hard hats, and set us free to see the fossils embedded in nearby slabs of stone.

Walcott carried off about 65,000 fossils after using an early paleontologist’s tool — dynamite — on the mountainside. But he and subsequent researchers left plenty behind.

Even with a thin layer of fresh mid-August snow covering almost everything, the fossils weren’t hard to find: a thumb-sized trilobite here, a fossilized wriggling worm there. Face to face with these creatures from unimaginably long ago, we were warmed with excitement on our 10-hour day trip back into geologic time.