In their workaday lives, they are are welders, carpenters, vineyard workers, laser light show technicians and elementary school students.
But in the hours beyond work and homework, a group of mostly men and boys are more often than not behind the controls of extreme rock crawlers, radio-controlled vehicles built for rough terrain.
"It's the most fun you can have going slow," said Tim Terry with Jake's Performance Hobbies, a shop in Rohnert Park.
Hosted by the shop, the rock crawlers took over a stretch of creek bed along the Prince Memorial Greenway between 9:30 a.m. and 1 p.m., under the Highway 101 overpass in Santa Rosa.
Sunday was the last hurrah of the city's Creek Week, a series aimed at promoting the area's waterways with organized clean-ups, educational walks to view fish and turtles, an underground tour of a downtown culvert and other activities.
The crawler controllers marked a series of obstacle courses through the riprap, the steep rock and concrete banks designed as erosion control that line Santa Rosa Creek, taking turns maneuvering their creations through the rough.
It's the usual spot for a cadre of more than a dozen hobbyists with the North Bay Rock Crawlers Club who devote hours, a fair amount of cash and their skills to building specialized vehicles with the agility to make it through the rock maze.
"It's too much fun to have a bad run," said Greg Nelson, 55, of Ukiah.
Nelson set his green rig at the start of the course and picked up his hand-held remote. Terry followed closely with a timer and clipboard.
"Six minutes on the clock, when you're ready," Terry said.
The goal is to drive through 10 "gates" marked with plastic knobs or tennis ball halves, maneuvering up, over and around the boulders.
It's harder than it sounds.
Vehicles are docked for going backwards and touching or knocking down a gate post.
About the size of house cats, the vehicles have fat tires and alterations that allow for agility and either four-wheel, rear or forward wheel drive.
Nelson was silent, his brow deeply furrowed, as he guided his green truck with a slow and methodical pace through the course. He lost a point when he had to reverse to get up a near-vertical ascent.
"If anyone can do it, Dopper can!" shouted AJ Rose of Sebastopol, calling Nelson by his nickname, Biker Dopper.
Up above the group on the Greenway path, Ken Hutchins snapped photos of the the competitors.
Hutchins, a civil engineer with the City of Santa Rosa's storm water unit, said he first spotted the rock crawlers several years ago and was thrilled to see people using the urban section of the creek for wholesome recreation. The city then asked them to show off the hobby as part of Creek Week.
"This was unforeseeable but pleasurable," said Hutchins of the sport. "They went through and picked up all the trash beforehand. They're good stewards."
Mike Keough, 57, of Truckee, said Santa Rosa Creek is one of his favorite spots to drive his rig.
Keough and a handful of other members of the Sacramento-based Backyard Boys Rock Crawlers traveled from Central Valley and foothill towns for Sunday's event.
"The best advice my dad gave me was, 'Son, stay a kid as long as you can,'" Keough said.