From the park compendium,
http://www.nps.gov/yose/parkmgmt/upload/compendium.pdf page 5
Except for Administrative Activities, Visiting Hours: Yosemite National Park is open 24 hours a
day, seven days a week except for the Hetch Hetchy area as described below:
36 CFR § 1.5(a)(1); 36 CFR § 1.5(f)
Hetch Hetchy Operating hours:
The Hetch Hetchy security gates will be open to vehicle, bicycle and pedestrian traffic
daily, during the following hours:
07:00 a.m. to 8:00 p.m. April 1st to April 30th
07:00 a.m. to 9:00 p.m. May 1st to Labor Day
08:00 a.m. to 7:00 p.m. Day after Labor Day to October 31st
08:00 a.m. to 5:00 p.m. November 1st to March 31st
Elevated Threat Level – The Hetch Hetchy security gates will be open to vehicle, bicycle
and pedestrian traffic daily, during the following hours and may be restricted further
based on security needs:
08:00 a.m. to 5:00 p.m.
Imminent Threat Level – The Hetch Hetchy security gates and the entire area around the
O’Shaughnessy Dam and the Hetch Hetchy Reservoir will be closed to public vehicle
traffic and visitation when the Department of Homeland Security issues an imminent
threat level warning to the nation or the O’Shaughnessy Dam and Hetch Hetchy
Reservoir.
The Superintendent has determined restricted access to Hetch Hetchy is necessary for orderly management
of the park and the security of associated facilities.
