Priscilla Navas and Victor Gonzalez stepped barefoot into the vat of mud and started squishing, as if they were stomping grapes.

But this was for a far different purpose. The Casa Grande High School freshmen were mixing cob, a sand-clay-straw mixture that their class is using to build two huge benches in their Petaluma school’s common area.

Miguel “Sir Cobalot” Elliott of Living Earth Structures in Sonoma County is leading science teacher John Shribbs’ classes in the project, part of a five-year transformation of Casa’s old football field — now in the middle of campus — into an outdoor learning center.

“It’s really cool,” said freshman Elizabeth Wilson, 15, as she heaped handfuls of mortar-like cob onto an adobe brick and sandbag substructure that will eventually become C- and G-shaped benches.

“We just finished learning about the rock cycle, so now it’s interesting as we work with the materials,” she said while helping other students to get the job done.

Earlier, other students removed loads of adobe clay soil from the old football field area to form an amphitheater. That clay was then repurposed into adobe bricks Shribbs’ students formed and left to dry two weeks ago.

Elliott, who specializes in building cob structures including houses, saunas, wood-fired ovens and usable art pieces, proposed using the abundant adobe soil to help connect the students with their natural environment.

“A lot of students are Latino,” he said. “They hear stories about families living in adobe or have visited family who live in adobe. But they haven’t worked with it.”

“I’m glad I’m doing this,” said Gonzalez, as his bare feet mashed straw into the wet clay. “I get to see the people enjoy this after we’re done. And it’s all natural. It’s from the Earth. There’s nothing in it that could hurt the earth.”

As she set broken pieces of concrete to help fill out the benches’ edges, Cenna Papola, 14, realized how much effort goes into building.

“There’s so much work and labor and time that goes into it,” she said. “It takes a community.”

Two other classes, including an Advanced Placement earth science class, are also working on the project, which is a small piece of the overall outdoor classroom, Shribbs said.

An outdoor kitchen has sprung up, with a donated Forno Bravo factory oven that Elliott and students covered in adobe and plaster, and a garden has been planted for the culinary arts program.

There is also an amphitheater, with retaining walls and seating, with a tile stage out front. Gravel paths lead through it with drip irrigation reaching the fruit trees and redwoods, Shribbs said.

Elliott will also help build a “cobzebo” shaded area as part of what Shribbs envisions as an inviting contrast to the asphalt elsewhere on campus.

On Thursday, as students built up the benches, they began connecting the lessons Elliott and Shribbs were teaching through the work.

“We actually made the bricks we’re using,” Wilson said.

“Our finished product is something we can use the next four years. And I have a younger brother who will use them, too.”

You can reach Staff Writer Lori A. Carter at 521-5470 or On Twitter @loriacarter.