How far would you go to stop urban sprawl? That’s the question of the hour in King County, Wash., where a private anti-sprawl proposal is pushing the conservation envelope on several fronts. At issue is a proposed $185 million purchase of second-and third-growth forest just east of Seattle. The land purchase by the Evergreen Forest Trust would be the most expensive private conservation deal in U.S. history and would protect a huge tract of land — 104,000 acres, or an area twice the size of Seattle itself. Sounds great, but there are several catches. First, parts of the land, all of which is currently owned by the timber company Weyerhaeuser, would continue to be logged for at least four decades, to help pay for the purchase cost. Second, the purchase would need special dispensation from the Internal Revenue Service or, failing that, congressional approval.