Welcome to SD! This time of year you have to look a little harder for stuff as the weather has heated up to the point where the majority of herps other than the heat tolerant ones such as the Red Racer and Striped Racer have turned crepuscular or nocturnal (meaning you have to look early in the morning or at dusk and at night) If you are in north county I'd just head east on highway 79 toward Mount Palomar, there are some sites along the way and there are quite a few habitats to search through. Once you cross over I-15 you get into some fairly rural areas and then it becomes national forest so there isn't as much private property. That or go south to Torrey Pines State Recreational Area, there are a number of interesting species there and it's more coastal so it remains cooler longer and the odds of finding something this time of year are much better. FYI, January through May are the best months here (from my experience) as you can find a lot of stuff board flipping and rock turning, I just did a 3 day jaunt in the south portion of the county and had to really work at it to find good herps (see my postings under HerpinDiego). Hope this helps a bit! If you have access to the military base there are some fantastic spots!!! The land there is as close as you are going to get to what it was like here 200 years ago, you may have to get special permission for some areas and it's been a long time since I was on base (you used to be able to get camping permits even as a civilian but I don't think they do that any more), just about any canyon that has semi-permanent water is a good start, search for oak tress and sycamore and follow the canyons, if there are rocky areas that's a good place to look as well and also along the fringes of grassland transition zones, but remember that most of the interesting stuff such as Crotalus viridis, C. ruber and C. mitchellii are going to be found in the late evening or at night this time of the year in most locations.
Good luck!!!