Only about one in five visitors to a national park site is nonwhite, according to a 2011 University of Wyoming report commissioned by the Park Service, and only about 1 in 10 is Hispanic — a particularly lackluster embrace by the nation’s fastest-growing demographic group.

One way the service has been fighting to break through is with a program called American Latino Expeditions, which invited Ms. Cain and her three colleagues. Groups like theirs went to three parks and recreation areas this summer — participants competed for the spots, with expenses paid for mostly through corporate donations — part of a multipronged effort to turn the Park Service’s demographic battleship around.

“We know that if we get them there, it can be transformative,” Jonathan B. Jarvis, the Park Service’s director, said in a telephone interview. A single positive park visit, he said, can create a lifelong pattern.

Easy to say, harder to achieve, Mr. Jarvis admitted. But the agency, in looking for a path forward, has also stumbled onto an unlikely team of allies — from outdoor outfitters to health and fitness advocates — all focused on the same thing: encouraging, supplying or simply understanding the young minority market.

GirlTrek, a national nonprofit group, organizes fitness-oriented park hikes for African-Americans. REI, the big recreation retailer, and Aramark, which manages lodging in some national parks, are sponsoring expeditions through the American Latino Heritage Fund of the National Park Foundation, a Congressionally chartered nonprofit group. New recruiting efforts to diversify the Park Service’s employee base — also largely white — are working with urban youth who might scoff at the idea of being a ranger in the wild, but could gravitate toward history, science or construction jobs.