RIO RICO, Ariz (Reuters) - Picking her way into the desert brush, Raquel Martinez gathered scores of plastic water bottles tossed in an Arizona desert valley near the Mexico border, often by migrants making a risky trek into the United States across increasingly remote terrain.
"We need more bags ... there's so much trash," said Martinez, one of scores of volunteers helping clean up the dry bed of the Santa Cruz River about 10 miles north of the Mexico border on Saturday.
Trash tossed by thousands of illegal immigrants as they chase the American Dream has been a persistent problem for years in the rugged Arizona borderlands that lie on a main migration and smuggling route from Mexico.
The problem was compounded as immigrants and drug traffickers responded to ramped up vigilance on the U.S.-Mexico border by taking increasingly remote routes, leaving more waste behind in out-of-the way and hard-to-clean areas, authorities say.
"Migants used to follow the washes or follow the roads or utility poles," said Robin Hoover, founder of the Tucson-based non-profit Humane Borders.
"Now they're having to move farther and farther from the middle of the valleys," he added. "They end making more camp sites and cutting more trails when they do that, and, unfortunately ... leave more trash."
Those making the punishing march carry food, water and often a change of clothes on the trek through remote desert areas that can take several days.
Most is tossed before they pile into vehicles at pickup sites like the one getting attention on the outskirts of Rio Rico, from where they head on to the U.S. interior.
"One of the problems that we are facing is that these sites are becoming more and more remote as law enforcement steps up its efforts," Henry Darwin, director of the Arizona Department of Environmental Quality, said of the flourishing borderland garbage dumps.
"There's probably sites out there that we haven't encountered yet or don't know about because there's a lot of people out in those areas," added Darwin, who gave testimony on the issue to state lawmakers earlier this month.
BACKPACKS AND WATER BOTTLES
There are no numbers to show exactly how many would-be migrants or smugglers take the illegal and surreptitious trek across the border into Arizona from Mexico each year.
But in an indication of the scale of the migration, federal border police made nearly 130,000 arrests last year in Arizona, where hundreds of Border Patrol agents, miles of fencing and several unmanned surveillance drones have been added in recent years to tighten security along the porous border.
With limited funding for clean up, Arizona environmental authorities draw on volunteers to help in drives like the one near Rio Rico, where an estimated 140 volunteers including residents, community and youth groups took part on Saturday.
Clean up efforts since 2008 by the department of environmental quality have included pulling 42 tons of trash from 160 acres of Cocopah tribal lands in far western Arizona, and clean ups at least seven sites on ranches and public land in areas south of Tucson.
Signs of illegal immigrants and even drug traffickers making the circuitous foot journey abound in the mesquite-studded riverbed near Rio Rico, a vigorous day's walk north of the border.
"I've found about a trillion water bottles," said David Burkett, a lawyer from Scottsdale, who worked up a sweat as he filled his fourth 50-pound trash bag. Nearby are tossed backpacks, food containers, a blanket and a pair of shoes.
He points out that alongside the apparent migrant trash is a large amount of other waste including a couch, kitchen countertops and yard debris, likely tossed by residents and contractors. Still, it is a shock to those living locally.
"We don't realize how bad it is until we come down and see it," said Candy Lamar, a volunteer who lives in sprawling, low density Rio Rico, as she works to pick up trash.
The area getting attention on Saturday lies a few miles from a remote spot where the bodies of three suspected drug traffickers were found shot to death "execution style" last November.
The area is not far from another out-of-the-way spot where Border Patrol agent Brian Terry was shot dead by suspected border bandits in December 2010. Volunteers working on Saturday were aware of the potential hazards.
As she stuffed a blue garbage sack with trash, retiree Sharon Christensen eyed discarded burlap sacking, blankets and cord -- the remains of a makeshift backpack of the type often used by drug traffickers walking marijuana loads up from Mexico.
"It would make me hesitant to come out here on my own, knowing that this kind of activity is going on ... It is a concern, and we need to be mindful," said Christensen, a retiree and hiking enthusiast.
Clean-up organizers liaise with Border Patrol and local police on security, in addition to warning volunteers of potential danger from snakes, scorpions or even bees that can swarm in discarded vehicle tires, and of potential hazards including medical waste and human excrement.
Equipped with gloves, volunteers such as Burkett, the Scottsdale lawyer, were glad to take part on Saturday.
"As an avid outdoors person in Arizona, I spend a lot of time using the desert," he said. "It's important to me personally to take the time to give back."
(Editing by Cynthia Johnston and Greg McCune)