YOSEMITE NATIONAL PARK — On a steep hill in Mariposa Grove, with enormous sequoias towering overhead, 12-year-old Marcella Tapia paused for a break.
A dozen other kids, dressed in "Yosemite Volunteer" yellow vests, dug and tugged and pulled out the roots of bull thistles, leafy green mullein and other invasive plants, huffing and puffing as they piled them up nearby.
"I don't like cleaning up my house," said a smiling Marcella, of East Palo Alto. "But I like cleaning up this house."
That sentiment is spreading in Yosemite, as increasing private donations are expanding programs that teach children -- particularly kids from urban areas who may never have visited a national park -- a variety of skills, from trail work to wildlife biology.
This year, more than 47,000 young people will participate in 30 programs at Yosemite, more than double the number of students from five years ago.
Much of the growth is due to a concerted effort by a San Francisco nonprofit group, the Yosemite Conservancy, which has tripled its annual spending for youth programs at the park in recent years, to $1.3 million.
The money is funding everything from Yosemite's popular Junior Ranger program to its Youth Conservation Corps, a group of 35 high school students who restored 30 miles of trails, replaced 175 campfire rings and installed 125 new picnic tables in the park last year.
"It's stunning the change you see in kids," said Mike Tollefson, president of the Yosemite Conservancy. "Kids learn about themselves. They learn about who they are. They go away with great life experiences, whether it's learning their role in doing the dishes at night or learning how to work with others. They learn about self-confidence and their own value away from home."
Tollefson grew up fishing and camping as a kid in Seattle, then worked more than three decades for the National Park Service, serving as superintendent of Yosemite from 2003 to 2009, and before that as superintendent of Great Smoky Mountains, Sequoia-Kings Canyon and Glacier Bay national parks.
Over the past 25 years, the Yosemite Conservancy, formerly known as the Yosemite Fund, was mainly known for raising private money to help the park complete high-profile construction projects. It raised $13.5 million in 1999 to rebuild the trails, bridges and signs around Yosemite Falls, and donated $1.8 million to renovate parking and landscaping at Tunnel View in 2008. The conservancy is spending $1.7 million to reroute trails, plant native willows and place new educational signs at Tenaya Lake.
Another nonprofit, NatureBridge in San Francisco, formerly known as the Yosemite Institute, has run programs for school classrooms at the park for 40 years.
But in this era of video games, cell phones and rampant childhood obesity, Tollefson, his board and supporters are on a crusade to spend more on human capital, too. Their goal is to bring more kids into Yosemite, particularly Latino, African-American and Asian-American kids who live in communities surrounded by traffic, crime and concrete, so they can tramp along trails, get their hands dirty and sleep outside. It's not just good for them, they believe, it's essential to the future of the national park system.
"We are trying to build long-term support for preservation and stewardship of public lands," said Don Neubacher, Yosemite's superintendent. "My view is one kid at a time."
Earlier this summer, Marcella and a dozen other kids from the Boys & Girls Clubs of the Peninsula participated in the "Parks in Focus" program, which educates middle school students about environmental science by giving them digital cameras, teaching them basic photography skills, and bringing them to Yosemite for five days.
The students from East Palo Alto and Menlo Park camped in Yosemite Valley and looked at Saturn's rings through a telescope. They spent two days at Wawona, and studied fire ecology, removed invasive weeds and learned about the park's history, from American Indians and Abraham Lincoln to John Muir. There were no cell phones, no texting and no video games allowed.
"My goal is to give them the opportunity to slow down," said Shauna Potocky, Yosemite's branch chief of education, "and experience who they are and to realize that people who they've never met saved places like this for them."
The grandeur of Yosemite -- and how different it is from his neighborhood in East Palo Alto -- wasn't lost on 12-year-old Luis Chavez.
"Our community isn't known for having a lot of kids go to college," Luis said. "But these kids here learn photography. They might want to become a professional photographer. Or maybe a park ranger."
Asked how the program had affected her life, 14-year-old Shontelle Watkins of Menlo Park grinned broadly.
"I'm coming back," she said. And a minute later, camera snapping, she headed up the trail.