ST. GEORGE, Utah - About 200 million years ago, a herd of dinosaurs walked through Sheldon Johnson's back yard.
And no one would ever have known if Johnson hadn't decided in February to level out a sandy hill, flipping over rocks to reveal what paleontologists are calling one of the best collection of dinosaur footprints ever found.
Johnson uncovered about 150 prints from several species, many of them so detailed you can pick out what appear to be scales between the creatures' claws.
''This is basically a snapshot of life in this part of the world about 200 million years ago,'' said Jim Kirkland, Utah state paleontologist.
Now, thousands of homo sapiens are making tracks to Johnson's front door to get a look at the footprints.
What they see is a rare early record of the first big meat-eater to show up in the age of dinosaurs, as well as tracks that may belong to a previously unknown species.
The tracks are scattered over more than a dozen 10-by-3-foot blocks of stone that Johnson, a 73-year-old retired ophthalmologist, overturned while using a backhoe to fill holes on his property. The rock naturally split into massive rectangles, with the upraised marks of the dinosaurs - not imprints but bumps - revealed on the flat bottom side.
Scientists believe that the 130 acres Johnson owns at the edge of this growing retirement city was once part of a great shallow lake. Where there are now red rock spires, mesquite trees and a new shopping mall, dinosaurs fed along the muddy shoreline, probably eating the bony carp-like fish found fossilized in the area.
Among them were the three-toed Eubrontes, a 26-foot plant eater that probably ate prehistoric ferns along the lake. Nearby, the 20-foot-long Dilophosaurus - the first big meat-eater of the early Jurassic period, easily recognized by the massive crest on its head - tiptoed along the shore looking for fish. As they crouched to grab their prey, some sank so deep into the mud they left imprints up to their elbows.
When the dinos walked away, their prints stayed intact long enough for sand to drift into the molds. Mixed with water, that sand created a sort of concrete, which then was covered with 200 million years of mud, clay and rock.
When Johnson unearthed the first pizza-sized print, which looks like the track of a giant, three-toed bird, he had no idea of the scientific significance. But he knew he had something big.
''When people ask me, 'What did you think?' I tell them, 'I don't know what I thought, but I'll tell you, I didn't sleep that night,''' he said.
He hasn't slept much since. Johnson and his wife, LaVerna, have been guarding the dinosaur rocks from dawn to dusk for the past two months.
As word of the discovery spread, dinosaur enthusiasts began arriving from across the country and even from South Korea and France.
''In two weeks, we've had over 12,000 people, and I haven't even had time to go check the guest book the last few days,'' said LaVerna Johnson, a poet and former schoolteacher who has become the family's dinosaur expert.
Clad in overalls and a broad straw hat, she welcomes visitors, as many as 1,200 a day on weekends, handing them loose-leaf notebooks with descriptions of the animals that lived here.
''This is magnificent. You can't hardly believe it,'' said Mark Manning of Ogden, who drove five hours from northern Utah to see the tracks.
The Johnsons' dream is to build a dinosaur museum in St. George, and they have promised to donate 20 acres to make it happen. The City Council supports them, and the local university, Dixie College, also has expressed interest.
''There are opportunities here that, if we do it right, will benefit a lot of people for a long time,'' said Kirkland, who will join Martin Lockley of the Colorado-based Dinosaur Trackers Research Group in St. George this weekend to continue the excavation and determine if some of the prints represent a previously unknown species of meat eater.
Kirkland said the Johnsons deserve praise for the way they have handled their find. Others in similar situations have tried to squeeze as much money as possible out of their discovery. The Johnsons don't even charge admission.
Sheldon Johnson, whose great-grandfather was sent to help settle St. George by Mormon church leader Brigham Young, said he can't imagine doing it any other way.
''We could make some money on it, we could sell each one on the Internet. But you know, one day the money would be gone and my great-great-grandchildren would not know a thing about the money,'' Johnson said. ''But they'll know about this.''