Two members of the Town of Danville Maintenance Department reported seeing the animal, which they said weighed about 90-100 pounds. Administrators at the school alerted Danville police and the two neighboring elementary schools, Greenbrook and John Baldwin.
"As soon as we got wind of this we had all of our students who were outside come in to the confined area of campus," said Terry Koehne, San Ramon Valley Unified School District spokesman.
When police arrived at the school they searched the area but couldn't find the mountain lion. They did, however, find a few opossum carcasses, leading them to confirm that the animal had been there.
The mountain lion didn't display any type of aggressive behavior, police said. In general the species is quiet, solitary and elusive. Mountain lion attacks on humans are extremely rare. The mountain lion is also known as a cougar or a puma.
There is a 6-foot-high fence separating the creek and the school. Koehne said it's highly unlikely the animal could get over the fence.
"Did we think it posed an immediate threat? No. But we always err on the side of caution," he said.
Police provided increased supervision at all three schools throughout the rest of the day. Teachers called the parents of any students who had walked or biked to school that day and offered to keep the students on campus until an adult arrived to pick them up.
Police also communicated with nearby residents, contacted homeowners associations, and distributed informational fliers. The California Department of Fish and Game will be monitoring the area to try to locate the animal.
"Our main concern was trying to make sure that students felt safe and secure," Koehne said.
There was to be increased supervision for the remainder of the week. Parents were asked to encourage children who typically walk or bike to school along or near the creek to take an alternate route.
Koehne said to the best of his knowledge there have been no animal sightings of this kind before.
"It's very, very rare," he said.
As a result of this sighting, Osage Station Park will be closed 8 p.m. to 8 a.m. until further notice.
* Do not approach a mountain lion.
* Call 911.
* Do not hike, bike or jog alone.
* Avoid walking or jogging when mountain lions are most active, at dawn, dusk and night.
* Keep a close watch on small children.
* If you encounter a mountain lion, do not run; instead face the animal, make noise and try to look bigger by waving your arms; throw rocks or other objects.
* If attacked, fight back.