Mammoths on the shore

Long before anyone farmed the lake bottom, the ground under Vineyard was the floor of an inland sea. And long before that, it was something else entirely.

The age of dinosaurs

The rocks of Utah hold one of the richest dinosaur records on Earth. Allosaurus, the long necked sauropods and dozens of species found nowhere else lived here between about 245 and 66 million years ago. Their bones are found mostly in the eastern and southern parts of the state, where the rocks of that age reach the surface. Under Utah Valley those layers lie deep, broken by the faults that lifted the Wasatch and buried under hundreds of feet of mud and gravel washed in by later lakes. No one is likely to dig a dinosaur out of a Vineyard backyard.

Their bones came to Utah Valley anyway. The Museum of Paleontology at Brigham Young University in Provo holds one of the largest Jurassic dinosaur collections in the world, and the Museum of Ancient Life at Thanksgiving Point in Lehi displays more than sixty complete skeletons. Within a few miles of Vineyard, some of the biggest animals that ever walked stand in the same valley.

Lake Bonneville

Then came the ice. During the last ice age, glaciers filled the high canyons of the Wasatch, and rain and meltwater filled the valleys of western Utah with Lake Bonneville. At its height, about 18,000 years ago, it was nearly the size of Lake Michigan. Utah Valley sat under hundreds of feet of cold, fresh water. Its waves cut the benches that still run along the foothills above Provo, Orem and Pleasant Grove.

The Ice Age safari

The shores of that lake were crowded with animals that would look strange today. Columbian mammoths grazed the lowlands. Musk oxen with heavy, drooping horns, close kin of the shaggy animals of the Arctic, roamed the valleys. There were giant bison with horns several feet across, camels, small wild horses, the giant short faced bear, and Jefferson's ground sloth, a lumbering animal the size of an ox. Paleontologists have found ground sloth fossils near the Point of the Mountain, at the north end of Utah Valley.

Most of what scientists know about these animals comes from the sand and gravel the lake left behind. Gravel pits along the Wasatch Front still turn up their bones. The first Ice Age fossil ever recorded in Utah was a musk ox skull dug up in 1871 by workers digging a cellar near Temple Square in Salt Lake City.

A horse in Lehi

One of the best finds came from just up the road. In September 2017 landscapers working on a backyard in Lehi uncovered the bones of an Ice Age horse. It was short and stocky, about the size of a large Shetland pony, and the paleontologist who studied it at the Museum of Ancient Life estimated from the sediment around it that it lived about 14,000 to 16,000 years ago, when the great lake was falling.

The lake itself was full of life. Its waters held trout, the ancestors of the Bonneville cutthroat that still swims in Utah Lake's streams, and suckers whose descendants include the June sucker, a fish found nowhere else on Earth. Snails lived in its shallows by the billions. Their small white shells are still scattered through the old shoreline gravels.

Those shells gave Utah its first written record of fossils. On October 2, 1776, a few days after leaving Utah Valley, Father Escalante noted fossil shells in his journal. They were almost certainly snails from the beds of Lake Bonneville.

The flood

About 17,500 years ago the lake cut through a ridge of loose rock at Red Rock Pass in southern Idaho, and a wall of water poured north into the Snake River. The Bonneville Flood dropped the lake about three hundred and fifty feet in a matter of weeks. The new, lower shoreline, called the Provo shoreline, is the broad bench that much of Orem and Provo now sit on.

As the climate warmed the lake shrank further, and by about 13,000 years ago it had broken into smaller lakes. The Great Salt Lake turned salty. Utah Lake, fed by the Provo River and other streams from the Wasatch, stayed fresh. Geologists date Utah Lake as a lake of its own to about 8,000 years ago.

What was left

The mammoths, camels, musk oxen and ground sloths were gone by then, and no one is entirely sure why. A warming climate and the arrival of human hunters both likely played a part. The people who came to Utah Lake after them found a shallow lake full of fish, marshes full of birds and mountains full of game, and they stayed. The friars, the pioneers, the dairies and the steel mill would all come later, on the shore of what was left.