EL PORTAL, Calif.—Ash from a wildfire that scorched 34,000 acres outside Yosemite National Park is now providing the perfect nutrients for hundreds of acres of California poppies and other wildflowers to bloom this spring.

The wildflowers carpeting the Merced River Canyon have brought carloads of gawkers to the narrow Highway 140 passage where the Telegraph Fire raged last July. Jan Van Wagtendonk, an emeritus researcher with the U.S. Geological Survey, says he has not seen such a brilliant display in four decades.