I'll give a +1 to red rocks as well for some day hiking.
I spent March 1 at Zion this year--yes it was technically winter, but the weather was perfect for hiking with highs in the low 60s. A couple areas were closed due to falling ice--including part of the Emerald Pools area--but I think it was worth the drive up since although not everything was open, it was not very crowded either.