Geologist began to study the area in 2008, after thousands of tons of rocks rained down on family-friendly Curry Village, flattening one of 17 cabins and sending schoolchildren scrambling for their lives.
"There are no absolutely safe areas in Yosemite Valley," said Greg Stock, the park's first staff geologist and the primary author of a new study that assesses the potential risk to people from falling rocks in the steep-sided valley.
After the Curry Village incident, the park closed one-third of the campground's 600 cabins. This week, 18 more will close, as well as all or part of five employee dorms. Also on the closure list: a half-dozen sites at Camp 4, a $5-a-night camping bargain near El Capitan used mainly by climbers.
A park representative said visitors with reservations in Curry Village this summer will still get rooms and that some cabins can be moved to safer areas.
Rooms at the Yosemite Lodge and the Ahwahnee Hotel are not in the danger zone. However, the Sierra Club's LeConte Memorial, a library and educational site, are.
Since officials began keeping track in 1857, 15 people have died and 85 have been injured by falling rocks in Yosemite Valley.
The Associated Press contributed to this report.