Nourished by two rainy seasons a year, it teems with hundreds of plant species, including towering saguaro, ocotillos and organ-pipe cacti, which in turn provide shelter and food for such animals as javelinas, bighorn sheep and speedy zebra-tailed lizards.
But since 1995, when the Border Patrol stepped up efforts to stanch the flow of immigration into California and Texas, Organ Pipe has seen ever-increasing damage from the thousands of migrants who have chosen Arizona as the best place to cross the border.
"Right now, (immigration traffic) is our most severe resource impact," says Organ Pipe's superintendent, Bill Wellman.
The most visible impact on the park is in the form of trash.
"There's an incredible amount of those (empty) plastic water jugs," says Mitzi Frank, a public information officer with the monument. "We find clothes, food cans, human excrement. We find blankets and shoes, even children's shoes."
The litter sparks numerous complaints from visitors, but park officials say it causes little permanent damage. More troublesome are the new paths carved by migrants trampling through the vegetation, compacting soil and hastening erosion. Officials say there are about a half-dozen major illegal foot routes, totaling more than 100 miles, in the monument now. Some follow old game trails that approach some of the monument's few water sources: tinajas, natural depressions where rock caches rainwater.
"At one of the water holes, we had an automatic camera set up," says Ami Pate, a biological technician with the park. "We got pictures of mountain lions, javelinas, and what is believed to be the first photo of an endangered pronghorn drinking. But the same camera also picked up illegals near the water hole."
The presence of people can scare away animals, putting them at risk during dry summers, she says.
In colder months, the migrants build campfires. "We've had several wildfires that are believed to have been caused by illegal aliens," says Frank. The fires don't spread in the fuel-scarce desert, she says, but when a saguaro is burned, it won't regenerate. And illegals looking for a place to rest often clear areas under mesquite or palo verde trees, destroying slow-growing saguaro seedlings.
Tens of thousands cross the monument each year. According to Border Patrol statistics, the number of illegals apprehended at Ajo, a town just north of Organ Pipe, rose from 851 in 1993 to 21,211 in 1999. Not all come on foot. Some drive across the border through a wire fence at the park's south boundary, where a park road is just yards away. Says Frank, "We can put up that fence and two hours later, it's down."
The Border Patrol has responded by increasing its presence within the park, an action that has mixed consequences (HCN, 9/27/99: Battered Borderlands). The extra officers have helped keep the number of immigrant fatalities down, says superintendent Wellman. But, he adds, "When you have 60 or 70 enforcement officers running around, there will be some impacts."