Approximately 50 Bay Area students and adults on a five-day educational trip in Marin County became ill Wednesday night and were sent home, a fire dispatcher said.
The affected students and teachers were part of a larger group staying at the Walker Creek Ranch, which is a campus of the Marin County Office of Education.
Reports told of at least one student from Danville in the hospital after attending the camp while 29 fifth grade students and one teacher from Tassajara Hills Elementary and four high school student counselors, including one Monte Vista High senior.
Outdoor school principal Mike Grant said that students from three Bay Area schools had been staying on the campus this week and that the illness seemed to spread equally among the schools.
The trouble began early this afternoon, Grant said, when "there were a few kids who were sick to their stomach."
He estimated that 52 or 53 people were afflicted with flu-like symptoms, including vomiting and diarrhea, and that the number of ill included mostly students.
From 2 p.m. until 10 p.m., that number swelled, and Grant said that with the input of Marin County health officials some healthy students were sent home as well.
"We decided that we had to get them home and get the bug out of the environment here," Grant said.
Some students were still on their way home as late as 3 a.m.
"It seems to be winding down, but it's been a pretty big afternoon and evening here," Grant said.
The source of the illness had not been pinpointed, Grant said, although it seemed to originate from one cabin. "We're assuming it's something viral that hit pretty hard and quick."
The ranch, which has been in operation since 1963, hosts fifth and sixth grade students, Grant said, with 200 students on average visiting the site every week for its 5-day residential science school.
The ranch, which is located at 1700 Marshall-Petaluma Road in unincorporated Marin County near Petaluma, is comprised of an outdoor school, conference center, and summer camp, according to the facility's website.
Students were visiting from San Ramon Elementary School in Novato and Redwood Day School in Oakland.