NOT LONG AFTER THE CIVIL WAR, prospectors swarmed into the San Juan Mountains of southwestern Colorado. Men with names like Dempsey Reese and Isiah Gunsolus staked out mining claims. Most of these prospectors eventually patented - gained full ownership of - these claims by doing minimal work and paying a small fee. 

Over the years, millions of acres were similarly privatized across the mountain West under the 1872 Mining Law. A handful of the claims held lucrative mineral deposits and were heavily mined, while miners built cabins or mills on others. Most, though, sat virtually undisturbed for over a century. 

But during the last decade or so, a new land rush has hit the West's high country. With desirable valley floors already spoken for, second-home owners are turning their eyes to the mountains above. Property values have soared, and hundreds of claims are changing hands. "No Trespassing" signs are popping up in local backcountry haunts, and rural counties suddenly face the unexpected headache of managing land use in places where the idea of building a house once seemed preposterous. 

In southwestern Colorado's rugged San Juan County, some 3,000 mining claims are scattered across more than 30,000 acres. For decades, most of that land sat untouched, visited only by hikers and sightseers. But after the county's last mine shut down in 1991, the claims took on a different luster. County assessor Judy Zimmerman illustrates the shift by pointing to a typical mining claim located on Red Mountain Pass. In spite of the fact that it sits above 11,000 feet and has only seasonal access, the claim sold as a home site late last year for $145,000; that, says Zimmerman, would have seemed outrageous a decade ago. 

Overall, the assessed value of the county's mining claims has gone up 300 percent since 1995. That has prompted both small and large sell-offs: Individuals have unloaded claims they inherited to make a buck or because they can't pay rising property taxes, and big mining firms have sold off more than 1,500 acres in claims since 1999. 

When long-vacant mining properties suddenly become real estate hot spots, officials can be caught off guard. "We didn't have a zone district prior to (1994) because we didn't believe these areas would be developed," says Ellen Sessano, long-range planner for Pitkin County, Colo. Home to Aspen and one of the first mountain resort areas in the West, Pitkin first saw people scrambling to "develop these sites in the middle of nowhere" less than two decades ago. With a big planning department experienced in dealing with development, the county was able to quickly implement special backcountry building regulations that limit house size to 1,000 square feet, ban utility extensions, and allow only one home for every 35 acres. Other Western counties, though, have nowhere near the resources of Pitkin, and are just waking up to the potential impacts. 

In Idaho, for example, Idaho County has plenty of patented mining claims ripe for development, yet not a lick of planning or zoning regulations. "Please don't mention that," says County Commissioner Jim Rehder. "I'm not a big regulation advocate, but I can see the benefit of developing a comprehensive plan." But he acknowledges that local sentiment leans against any sort of regulations or planning, a common trait of former mining communities. Until the community starts to see the results of a lack of regulations, he says, there won't be any push for county government to lay down new laws. Already, there has been a surge of second homes - nearly 40 percent of the county's property tax bills are sent out of state. And in a nearby county, a 30,000-square-foot vacation home, complete with helipad, sprouted out in the forest. 

Down in San Juan County, after decades of a laissez faire approach to mining claim development, commissioners implemented stronger regulations and a review process for new building. It hasn't stopped development: More than a dozen houses have been built in the backcountry in recent years. It's a flurry rather than a blizzard, but in a county that sits mostly above 9,000 feet, even that can have big impacts. County officials have grappled with everything from people wanting to build houses on avalanche-prone slopes to landowners knocking down historic mining structures. 

But perhaps the biggest problem is what happens when land considered public by locals suddenly sells for big bucks. In San Juan County and many other mountain counties, roads and trails commonly cross private land. When absentee mining firms owned the parcels, people often hiked, camped and even held weddings on them without fuss from the owners. But when landowners put down $100,000 or more with plans for building a mountain retreat, they are more inclined to block roads and trails. This doesn't sit well with many rural counties, but local governments often lack the legal means to stop it, says Gabe Preston, a Durango, Colorado-based planning consultant for rural communities. "The ownership of road access in the public/private patchwork is not well documented," Preston says. "It's a real headache trying to prove clear legal ownership of easements." San Juan County has mostly kept its roads and trails open by using historic records and aerial photos; occasionally, it resorts to bulldozers and bolt cutters. But in neighboring San Miguel County, Wilson Peak, a popular fourteener, was virtually off-limits to climbers for three years after a landowner cut off access to a trail crossing his land. 

The Alpine Loop is one road that probably will never be closed by a landowner. It winds its way through 65 miles of the San Juan Mountains, topping out at more than 12,000 feet. Each summer, thousands of people travel the rough unpaved loop in four-wheel-drive vehicles to see pristine mountain views and the remnants of old mining camps. Most of these visitors assume that the fields of wildflowers and high peak panoramas are federal land, to be preserved in perpetuity. But they're wrong. Much of what they're driving through is actually private property staked out by prospectors long ago. 

Not far from one of the highest points on the loop, where 13,000- and 14,000-foot peaks form a stunning backdrop, "For Sale" signs mark a dozen claims totaling 100 acres. One of them, the Palmetto, is priced at $95,000. It's advertised as including "high alpine tundra" along with "numerous building sites and 360 degree views." 

Halcomb writes from a fire lookout in southern Oregon and Thompson is HCN's associate editor.