Just check out the offical website;
A short section of the Valley Loop Trail at The Ahwahnee is closed due to rockfall risk, although a short detour is available.
The John Muir Trail between Clark Point and Panorama Trail junction (near the top of Nevada Fall) is closed due to dangerously icy conditions and a significant rockfall. It is possible to hike to the top Nevada Fall via the upper portion of the Mist Trail.
Further notes: At 11:23 pm on April 15, a large rockfall occurred from the slope above the John Muir Trail between Clark Point and the top of Nevada Fall, sending hundreds of boulders onto the trail. Nearly 1,000 feet of trail are covered with boulders, trees, and other debris.
The trail will require significant repair, including drilling and blasting of large boulders. Geologists are now assessing the potential for additional rockfalls. The trail, which was already closed for the winter season, will be closed for at least several more weeks. A reopening date is not known at this time.
Gates are closed across the John Muir Trail at Clark Point and near the top of Nevada Fall. For your safety, please do not enter the closed section of the trail.
Each year the valley and cliffs around it experience geological changes.