You know it's a popular hike when you pull in to the trailhead and there is a guy there directing cars on where to park. As others have said, the flowers are prolific, as are the people. The bloom is at its peak.
Here are some of the many flowers we saw: Balsamroot, larkspur, phlox, popcorn flowers, chocolate lilies, currant, palmate coltsfoot, early columbine (no bloom), wild roses, starflower, woodland stars, chickweed, hooker's fairybells, miner's lettuce, wild strawberry, salmonberry (no berries yet), fringcup, three leaved anemone, sedum, thread leaved phacelia, triteleia, vetch, pea flowers, vanilla leaf, buttercup, parsley, shooting stars, big headed clover, sea blush, trillium, death camas, and lupine. Just to name a few.