Southeastern Utah, around Moab, is in season at that time. Distances between towns are huge, it is quite hilly, sometimes windy, and you have to be aware of where your next water is available. I haven't toured there yet, but have spent a lot of time in the area rock climbing, and I think mid to late march is perfect - just starting to get hot. Canyonlands Nat'l Park, Arches Nat'l Park, Castle Valley, the Colorado River, south to Monticello via the La Sals, the Abajo's... scenery is unreal.
Logistics could be troublesome, Moab has a tiny airport, I don't know if you can actually get a commercial flight there. Salt Lake City is 5 hours drive. There is a shuttle bus from SLC to Moab, that might work.
Central/Southern California can also be nice that time of year, but you can still get a pacific storm, so you would want to be prepared for that. You could do a loop from Santa Barbara or San Diego (Julian, Hemet) or Palm Springs (Joshua Tree National Park).