Random apartment w/o notice search leads to city inspection. Is this legal?

I rent an apartment in an apartment complex in California. Regular apartment lease (no public housing, HUD, subsidized, or anything like that - just a regular apartment). I am a single guy living by myself. I am usually a neat person, but like anyone else sometimes I let my place go for a week or so if work stresses are high, not expecting any friends over, and I didn't have time to clean up everyday. I admit, my place was not in the greatest shape but one day I came home and all of the lights in my apartment were off and my patio door was open. I NEVER turn all of the lights off (even when I go to sleep) let alone leave the patio door open. I was kind of pissed as I suspect this has happened once before (but could not prove it). Anyway, 2 days later I get a notice taped to my front door that the rental management and the city needs to perform an inspection on my apartment. I cleaned up my place, of course. They came, I wasn't there, and again all of the lights were off when I got home but they left no doentation as to what was inspected and what was found. I called the rental office who confirmed that inspection took place but act aloof as to what was inspected, why, and results of the inspection. Is this legal?