Depends where you are. In much of the Valley you will not see a cab anywhere, but you might be able to call one.

In SF proper, there are more cabs, but don't forget the hour-long waits we had before the ride-sharing thing started. I don't know if it'll get that bad again, but I don't think they authorized thousands of new cabs like (IMO) they should have. Also, I've had cabbies in SF tell me point-blank they won't take my fare because it's not far enough. Yeah, illegal, they don't care.

Further out... good luck. You're in Concord and need a ride to Walnut Creek? Might work, but it might be faster to try Craigslist.