Among park volunteers, Big Bend is considered one of the best opportunities. There's a healthy volunteer community here, with a monthly newsletter and constant email dispatches describing events like group triathlons and moonlight bicycle rides, a hiking club, a seasonal awards banquet and community recycling days. Perhaps most important, the volunteers feel accepted by the paid employees.

Not every experience is idyllic. I spent several months before Big Bend doing a volunteer stint in Denali National Park as part of the Exotic Plant Management Team -- in other words, on weed patrol. I wandered Denali parking lots with a GPS, pulling dandelions, and on field weeks, I strapped on head-to-toe anti-mosquito clothing, including a hooded shirt with a built-in mesh faceplate, and roamed the endless shrubby dwarf birch in that park's swampy west end. While the Denali botany crew was supportive and lively, I struggled to break into the larger community of employees and volunteers in the Great North. Big Bend came as a pleasant surprise after that.

Our morning briefing in Santa Elena Canyon is short and to the point: Safety first, trash second. Avoid landing on the Mexico side. The river is shallow here, so we'll probably do some boat-pushing. Skip Jiru, a volunteer with the maintenance division, jokes about canoe-assisted hiking and gets a few chuckles. Brachman and I have hiked with him out to remote archaeological sites and up into the Chisos Mountains, which rise higher than 7,000 feet, to inspect backpacking campsites and make sure all the bear boxes are in working order. When it comes time to push off, Jiru paddles his canoe over a shallow turn with an enthusiastic whoop.

A day trip on the Rio Grande can cost more than $150 a head if you go through local guiding companies, but we volunteers get it free as part of the river cleanup. Today's stretch runs along the base of a huge mesa on the Mexican side that drops abruptly to the river in 1,500-foot limestone cliffs.

We stop on a wide sandbar for lunch and redistribute some of the tires we've dug out of the sand. We've got six tires so far, but we're hoping to break the record: 13 for this stretch. Somewhere upstream a while back, a rancher tied over a thousand tires to his portion of the riverbank in a vain attempt to control erosion. The big flood in 2008 had other ideas: The Mexican dams on the Rio Conchos tributary opened their waterways full-bore to let that flood rage, and now the tires keep showing up on sandbars and riverbanks in the park. Each year, volunteers come back and fish out a few more.

Our river cleanup ends on a muddy beach. I jump out and sink up to mid-thigh in mud and water. We wrestle the canoes onto the bank and unload piles of trash and 14 tires -- a new record! On the way back to the park's small residential neighborhood, we drive through the creosote-filled Chihuahuan desert, skirt a smaller canyon lined with volcanic ash, bump over a few lava dikes and stop at a historic trading post -- almost a hundred years old -- for ice cream, because, after all, it's November in Texas and we're all hot, sweaty and sunburned.

A few days before Christmas, the Catons knock on the door of the funky doublewide trailer that houses Brachman and me, across the street from the retirees' RVs. They propose a Christmas party for all of the spare volunteers in the area: "Us orphans have to stick together." Since many of the park's paid employees take their annual leave over the holidays, a good deal of the work this time of year falls to volunteers.

On Christmas day, we host eight volunteers and two park employees in a potluck dinner in our trailer, where we've wrapped our living-room window with a string of festive chile lights. As the eggnog and the pot roast disappear, the conversation turns to the park itself. Riley Caton asks the group of gray-haired retirees, including a former preacher, a former nurse, and a former journalist: "If you had it all to do again, what would you change?" One by one, they all answer with some version of: "I wish I had volunteered with the Park Service sooner."

Henry Ring is a freelance writer and conservation volunteer with roots in Montana, who is temporarily based in Washington, D.C., as one of the countless unemployed 20-somethings looking for a paid job in the Great Recession.