Everything but the traffic and lodging is bursting at the seams during spring—specifically, April and May—in Yosemite Valley. Waterfalls swell with snowmelt from the mountains, dogwoods are in bloom, and wildlife begins to stir. Hike in the lower elevations, visit the waterfalls, picnic in El Capitan meadow, and watch rock climbers on the big wall. Feeling adventurous? Spend a day basking in the sun while you take rock-climbing lessons in the sports mecca.  —Jennifer Duffield White Read…