What plant is that?

Our Mystery Plant for March blooms in spring on cliffs, ledges and rocky areas. With a basal rosette of attractive egg-shaped leaves, and branched cluster of brilliant white flowers this 4-to-12 inch tall plant makes a good rock-garden ornamental, and it is easy to identify in the wild. (Note: the Genus has changed since Newcomb’s Wildflower Guide was published in 1977, so please search GoBotany before submitting your guess.)