The numbers are big: nearly 93,000 acres, 144 square miles and a half-million new Wasatch Front residents in the next 75 years.

And behind it all is a fairly young company, Kennecott Land, the little sister of mining company Kennecott Utah Copper. Formed in April 2001 by Rio Tinto, the international mining company that owns Kennecott's mining arm, Kennecott Land now has just over 50 employees.

Since the early 20th century, Kennecott has been mining in the Oquirrh Mountains, accumulating a mass of land not just for mining but also for tailings ponds, transportation, buffers and other uses. That land — now almost 93,000 acres, with about 79,000 of those acres lying in Salt Lake County — is the largest metropolitan landholding by a single owner in the United States.

And it's just about ready for the next phase.

As Kennecott's mining operations wind down and change focus, the land is no longer needed to support that use. So Kennecott Land was created to figure out just what to do with the property, Kennecott's "asset in addition to mining," Kennecott Land President Peter McMahon said.

There were options. Kennecott Land could have sold the acreage off in chunks to developers to build their own subdivisions, commercial developments, office parks, industrial zones and any other variety of uses. Or Kennecott Land could opt to plan and develop the whole thing itself. The company went with the latter option.

"It made more sense to keep it in the family, so to speak," McMahon said.

The result has often been called "unprecedented" — a countywide effort to master-plan the entire development, drawing off ideas discussed in four summits held since August. The summits have brought together county planners, officials from nearby cities, environmentalists, transportation planners, public utilities and a host of other interested parties, all to gather input and guide Kennecott Land's vision for the next 75 years.

"The land is large," McMahon said. "We're not just a developer with 500 acres. . . . If you're building at this scale, you can't do it without engaging the community."

And it's a big community that's involved.

"This Kennecott project doesn't just affect Kennecott and that 93,000 acres," county Mayor Peter Corroon said. "It affects the whole county. We're talking about another half-million people moving to the valley in the next 50, 60 years."

The land

Not since the early settlers arrived in the Salt Lake Valley has there been so large a clean slate for development, Kennecott Land officials are fond of saying. And rarely has there been anywhere in the United States such a large-scale plan for tackling so huge a piece of undeveloped property.