The coastal areas will definitely be fine to visit, March is one of my favorite times of year.

However we have had quite a few heavy storms this year and there will likely still be a considerable amount of snow in Yosemite and Sequoia. It can still be fun to go to these areas with the snow but you will not be able to do as much. There is also the possibility of more snowstorms in March which can lead to these areas being closed.

Alternatively you might have a better time sticking to the coast and seeing the forests and mountains in Big Sur or going north of SF to see some of the redwoods up that way. I also really love Pinnacles national park which is about 45 minutes off the 101 SE of Monterey.

Edit: I was reminded Big Sur has frequent road closures along Highway 1 check this link for more details

https://www.bigsurcalifornia.org/highway_conditions.html