San Diego rides
If it looks like you will be heading south, pm me and I can give you a list of routes to take out of San Diego, Imperial County etc. March should be good weather.
You didn't say how much time you will have, but there are at least a weeks worth of rides just in the local area. Hot springs, Slab City, Palomar Mountain, Agua Caliente, Corrizo Gorge and Idyllwild are just a few you can look at. Ocotillo Wells and the Temecula Wine Country as someone already mentioned as well. Don't overlook the coast along San Diego County, the Cabrillo Monument, Sunset Cliffs and Torrey Pines are also worth your time.
'02 BMW R 1150 GS-A, '07 BMW G650 X-Challenge, '08 BMW G650 X-Country, '09 BMW G650 X-Country, '03 KLR 650, '04 KTM 400 EXC, '02 Kawi KDX220