Utah circa 15,000 years ago:

Arctic glaciers finger their way into the Great Basin out of the frigid north. Pleistocene mammals - saber-toothed tigers, mammoths, giant sloths - roam the shores of the giant freshwater lake that covers most of the state. Cave-dwellers in search of game have wandered into Utah, but for the most part, man still lives in southern Idaho along the shore of the huge lake and along the Snake River.The lake swells with the melt of the Ice Age, reaching 5,090 feet above sea level. Then one day, the lake's northern outlet through a natural dam near modern-day Preston, Idaho, collapses, unleashing a flood of water down the Snake River that exceeds the cumulative total of all other rivers flowing to the ocean. Boulders the size of houses are carried as far downstream as Boise.

The lake level drops hundreds of feet over the years ahead. The behemoth lake begins a steady recession - a decline accelerated by a changing climate. By 4,000 to 5,000 years later, the lake level has steadied at 4,280 feet - a faint shadow of its former self.

The falling lake levels brought man - hunters, gatherers, wanderers - to Utah. With man came civilization and eventually man's crude and rarely successful attempts to control what is now called the Great Salt Lake.

Through its long and storied history, Antelope Island has stood as a sentinel over millennia of geological change. It has stood above Lake Bonneville, watching as the lake rose and fell, as earthquakes changed the face of the landscape and erosion took its toll on layer after layer of strata.

Changes covering millions of years are etched in the rocks of Antelope Island, and Monday and Tuesday Utah lawmakers got a first-hand look at the unique geology that will play an integral part in the development of Antelope Island State Park.

"Studying and gathering the interpretive data is a preparatory step toward reopening the island to the public," said State Parks and Rec-reation Director Jerry Miller. "When it is reopened, we want to be able to present the unique geological resources as part of the Antelope Island experience."

That unique geology includes pioneer-era slate mines, pristine sand beaches and the oldest rocks in Utah, estimated to be 2.9 billion years old.

At the invitation of Miller, the state Geological and Mineral Survey spent several months surveying the island and collecting data that will be used to assist in the development of the island as a state park and to provide an interpretive experience for park visitors.

By studying the lake's history, "We can better understand that the past is the key to the present," said geologist William Case. "If we understand what happened in the past, we can better choose where to build now and where not to build."

For example, geologists have determined that nothing should be built on Antelope Island below the 4,217 foot level. The lake currently stands at about 4,209.

"Where does a gorilla sleep? Anywhere he wants to," said Genevieve Atwood, director of the Utah Geological and Mineral Survey. "In this case, the lake's bed is 4,217 feet, and you must respect the lake up to that level."

The state is preparing to reopen the island to the public in 18 months. Determining where to build roads, which springs to develop and if the island can handle large-scale tourist accommodations are all issues addressed by the UGMS study. Critical decisions as to the development of the island, which will take several years, will be made as money is made available by the Legislature.

A new visitor center is on the drawing board and transplants of elk and antelope herds are planned over the next couple of years. Hotels on the island's north arm are a possibility, as is the renovation of a pioneer ranch on the east side.

"We want to make Antelope Island the premier attraction in the state," said Jay Christianson, northern region manager for Parks and Recreation. "If we do it right, it will be on par with the national parks. It adds a whole new dimension to Utah tourism."

Some 800,000 to 900,000 people visited the park the year before the state closed the causeway, and that was when the state had only the beaches and picnic areas to offer. Now, the state owns the entire island with its impressive deer and buffalo herds, mountain terrain and scenic vistas.

Lawmakers have long dreamed of Antelope Island as the state's premier tourist attraction, and those that participated in the field trip were more than impressed with the potential of Antelope Island.

"We own a Jewel of the Nile right here in our own back yard," said Sen. David Steele, R-West Point. "It is a hidden reservoir of opportunity. I am impressed and encouraged by what is being done here. I'm convinced it can be a key part of the long-term economic development of the entire state."