RIPON -- A red-shouldered hawk circled high above the trailhead at Caswell Memorial State Park, calling out, it seemed, to the dozen or so people headed into the forest.
The high then low squawks rained from above the valley oaks, from above the swallows that rolled in the air, from above a bend in the Stanislaus River.
"That's a good place to start," said Guy Van Cleave, a professor of biology at Columbia College, pointing up to the hawk. "You hear a lot of sounds out here that have nothing to do with McHenry or Highway 99."
Great Valley Museum celebrated the 19th annual Tule Fog Fete in Caswell on Sunday -- a celebration of nature, conservation, science and the end of winter fog. The thick valley fog -- tule fog -- usually disappears around the close of February or early March. Fete is the French word for festival, and for this event is a play on "feet," which were part of the fete's first logo -- a goose coming in for a landing, feet out.
Dozens of feet marched behind Van Cleave on Caswell's River Bend Trail and stopped when he stopped to point out the features of riparian forest and oak woodland. This riparian forest is a rich riverside landscape of cottonwoods, willows and alders. Behind where they stood, one step removed from the river, the dark dense acreage of oaks makes up the woodland.
"You can relax, feel the blood pressure dropping, that headache developing on the fringe seems to evaporate," Van Cleave said approaching a bend in the river. "Everyone needs that. You don't have to be a nature lover to appreciate it. That's why we need places like Caswell."
Flanked on all sides by agriculture, Caswell is 258 acres of what the valley looked like before plow teams and planting.
"This is what the whole valley looked like at one time," said tour-taker Veronica Falcinella with 9-month-old daughter Angelina on her back. "Can you imagine?"
Earlier in the day, Van Cleave manned the owl table. Kids dug through owl pellets -- walnut- sized balls of fur and bones that owls vomit up after every meal. The pellets look like something that would clog your sink.
There was a salmon fun-run for children sponsored by the Tuolumne River Trust, with stations that mimicked real-world obstacles such as waterfalls, bears and fishermen. There was a dessert auction, the bluegrass Zero Visibility Band and an obstacle course designed by Boy Scouts Troop 14 from Modesto. The Stanislaus Wildlife Care Center had Oscar the burrowing owl, Carson the red-tailed hawk and Mimi the merlin falcon on display.
The turtle and tortoise table was especially popular.
"They are so cute!" said Courtney Rarick, 14, a baby turtle in hand.
A yellow-foot tortoise, bigger than a football, crawled under the table, and a California desert tortoise -- an endangered species -- burrowed in a small glass aquarium.
"The real problem with turtles," said Sarah Smith, a traveling teacher with the museum, "is turtles as pets."
The No. 1 offender, the red-eared slider, seemed innocent enough, swimming in a bowl next to his endangered cousin.
At the size of a quarter, slider babies are popular at flea markets and pet stores, but few expect them to grow to the size of a dinner plate in a few short years. It might seem kind to release them into a nearby lake or stream, but red-eared sliders aren't native to California -- they're from the Mississippi River and the southeastern United States -- and create problems for the native and threatened western pond turtle.
Native animals in natural areas are what places such as Caswell and the Great Valley Museum strive for -- fog or no fog.
Bee staff writer Michael R. Shea can be reached at email@example.com or 578-2391.