For the first time in almost 100 years, a rare frog population is having sex in the Santa Monica Mountains

A rare species of frog that all but disappeared from the Santa Monica Mountains nearly 100 years ago has been found breeding on its own again in the coastal range, officials announced Wednesday.

National Park Service rangers and scientists who surveyed the mountains’ mossy, muddy creeks on March 14 found nine egg masses belonging to the California red-legged frog, a species popularized by Mark Twain’s “The Celebrated Jumping Frog of Calaveras County” in 1865, Park Service officials said.

A single egg mass can contain 1,000 to 3,000 eggs, said Park Service ecologist Katy Delaney, who spearheaded the frog’s replenishment program.

The egg masses were likely laid by newly matured frogs that were part of the first class of eggs the Park Service introduced into the wild in 2014. That year, scientists took about 350 eggs from the only known population of red-legged frogs in the mountains, a small group located in the Simi Hills, to the north, and put them in a protective pen in a stream where they eventually hatched and were released.

Since then scientists have relocated batches of eggs from the Simi Hills population in groups of 400 to 500 every year and placed them in four locations across the Santa Monica Mountain range — one on the western edge of the mountains and three in the central area, Delaney said.

The egg masses found last week are the first sign the population is sustaining itself without human assistance, Delaney said.

“I don’t think it’s too much to stay that this could be the start of a comeback. This would’ve never happened naturally,” Delaney said, before joking, “They would’ve never gotten across the freeway the way we drive them.”

According to the Park Service, the California red-legged frog nearly vanished from the Santa Monica Mountains in the 1920s and 1930s when ranchers introduced the invasive crayfish, a 3-inch-long crustacean that’s used as fish bait and eats fish, insects, eggs, tadpoles and everything in between.

A single red-legged frog was spotted in the 1970s. In 1999, the first population of red-legged frogs was found in Simi Hills and contained about 100 adults, Delaney said. Only two other populations of the species are known to exist in Los Angeles County and neither one is in the Santa Monica Mountains, the park service said.

The red-legged frog is the only species missing from the park’s ecosystem and because the species is so sensitive to its environment, experts view it as an indicator of the ecosystem’s overall health, officials said.

When the surveyors revealed their discovery to Delaney, “there was a lot of shouting, whooping and high-fiving,” she said. “I’m really happy for every single milestone, but this is sort of the one we’ve been looking for.”

Park officials declined to specify where the egg masses were found or where the other relocation sites were so they could remain undisturbed by humans. Park scientists will relocate more eggs from the Simi Valley population in the spring and if they receive more funding, in the years to follow, Delaney said.

joseph.serna@latimes.com

For breaking California news, follow @JosephSerna on Twitter.