Permits now required to climb Yosemite's Half Dome

If summiting Half Dome is on your bucket list of the things to do before you die, better book the hike now.

Alarmed by the deaths of four climbers on the world famous granite monolith since 2006, the National Park Service yesterday started requiring hikers to reserve permits to climb to the top of Half Dome on busy summer weekends and holidays.

"This has become a serious safety issue," said Kari Cobb, a park spokesperson.

The result: Permits for weekends and holidays in May and June sold out in 15 minutes after being put up for sale yesterday morning at 7 a.m.

Aspiring climbers can reserve permits for similar periods in July and August starting April 1 -- and for September and October starting May 1 -- by visiting the park service's online reservations service, or by calling 877-444-6777.

Park officials recommend that travelers set up a profile on the site several days before permits go on sale and sign on immediately at 7 a.m. the day the permits become available. There is a $1.50 processing fee.

Serious climbers who summit Half Dome routinely said they've been surprised in recent years by increasing crowds on the mountain.