Just three miles north of Arizona's border with Mexico, the Coronado National Forest is littered with the leavings of people on the run: empty plastic water bottles, opened tuna fish cans, sweatshirts, jars of foot powder. Near a scattered pack of playing cards, some turquoise underwear lies in an undignified tangle.

A pair of small pink Mary Janes, the heels squashed down, sprawl a few yards away. Together, they are some of the remnants of hundreds of illegal immigrants and drug smugglers who cross this mountainous landscape every day. It's hot and dry and the wind is a terrible nag, blowing trash and red dirt around to no obvious end.

"Every hundred yards you see this amount of stuff," says Heiko Bornhoff, a special agent with the U.S. Forest Service. "It's just a mess."

This week, the Senate is debating what to include in a massive immigration reform bill. Most of the national discussion has centered on the undocumented immigrants who live in the United States and how to stem the flow of illegal traffic at the border. Almost entirely missing from the discussion, however, is the impact that the thousands of border crossers and their American pursuers have on the landscape.

Since the Border Patrol significantly closed down access to crossers in cities such as El Paso, Texas, and San Diego, Calif., a decade ago, illegal immigration has been funneled onto over 350 miles of public lands along the Arizona and California border. The increased activity has meant that wilderness areas and wildlife refuges are about as untrammeled as a city park. Some argue that environmental damage is a minor concern when measured against the cost of human lives and global economics, but the harm to land and wildlife is obvious and growing. Immigrants and Border Patrol agents have carved a maze of trails and roads into the fragile desert sand, and according to a 2003 GAO report, "destroyed cactus and other sensitive vegetation, including habitat for endangered species."

Fire is another concern, for as immigrants make their steady way across the arid land, many will light small fires under trees for warmth, to heat food or as a call for help. These fires aren't Boy Scout-caliber, with a ring of rocks to prevent cinders from escaping. As the wind blows through long after the immigrants have left, some smoldering fires can spring to life. Fires that spread at the wrong time of year — when humidity is low — are of high intensity and have destroyed Douglas Fir and oak forests where the endangered Mexican spotted owl survives. After fires like this, it takes hundreds of years for the forest to regenerate, says Glenn Frederick, a Coronado Forest biologist based in Sierra Vista, Ariz.

The cat-and-mouse activity at the border is also limiting scientific research. Frederick and other biologists say they have had to change the ways they study populations of species because it's dangerous to be out in the field alone or at night.

Actions of the Border Patrol add to the problem. According to a report released last spring by the nonprofit Defenders of Wildlife, for the last two years Border Patrol agents have been allowed to ride off-road vehicles anywhere they want across public lands. They can also build roads and backcountry "enforcement" camps in wilderness areas. The Border Patrol never completed analyses for this unfettered freedom on public lands as required under the Endangered Species Act or the National Environmental Policy Act. Moreover, legislation passed last year allows the secretary of the Department of Homeland Security to exempt the Border Patrol from all federal, state and local environmental laws when constructing walls, fences and roads along the border.

An amendment proposed by Wyoming Sen. Craig Thomas, R, to the immigration reform bill currently under debate takes some steps towards protecting our borderlands. Agents would undergo training in how to minimize the effects of security operations on the landscape, border monitoring would be increased for sensitive areas, and the agency as a whole would be required to come up with a strategy for protecting natural resources.

Rebecca Clarren is a contributor to Writers on the Range, a service of High Country News (hcn.org). She writes about labor and immigration issues in Portland, Oregon.