SONORA, Calif. — Four adults were injured and one remained unaccounted for after a large oak tree fell Wednesday at a summer camp near Yosemite National Park, authorities said. No children were hurt.

The tree took down power lines but did not fall on any buildings at Camp Tawonga in rural Tuolumne County, sheriff's spokesman Sgt. Jim Oliver said.

He did not know the severity of the injuries to the adult staff members, who were taken to hospitals. Sonora Regional Medical Center received two women ages 20 and 21 with minor injuries, spokeswoman Gail Witzelsteiner said.

Oliver said the power lines were grounded and fire crews were working to remove the tree to make sure no one was underneath.

Authorities received calls about the mishap around 8:25 a.m. The camp was continuing activities as parents were informed.

There are about 300 campers and 150 staff at the facility that offers sessions for students in 2nd grade through 10th grade. The camp is located on 160 acres in the community of Groveland in the Stanislaus National Forest.

It has been in operation since 1925, according to its web site.