The Yosemite area is home to hundreds of varieties of wildflower, with dozens more clamoring to get in all the time. The great bloom-off starts in Hite Cove, a few miles outside the park at around 2,000 feet elevation, in late February or early March, and for the most part spreads like a stadium wave from low to high elevations, hitting Yosemite Valley and Wawona Meadow Mayish, brightening the meadows along the Glacier Point and Tioga Roads in June and July, and hanging on at high elevations like the Gaylor Lakes basin as late as August. In case you weren't keeping track, that's a six month window of wildflowers. If they're what you're after, you can hardly miss.
In case you're a book lover (and what right-thinking person isn't?), there are several Yosemite wildflower guidebooks available.