Chickens that are originally from the Mediterranean or Middle East will do best in San Diego. One way to figure out where a chicken breed came from is to look at the combs. Breeds with larger combs were developed in hotter climates, as chickens use their combs to dissipate excess heat. Your Leghorn is a Mediterranean chicken and will tolerate heat better than the others.
 
I would still not keep him, however--no matter how pretty. My brown Leghorn pullets didn't lay their first eggs until they were a full year old. I finally gave them away for free to a woman who had lost her flock. If you look them up, the brown variety of Leghorns is reputed to not lay nearly as well as their white cousins, so it's not just me. Even the descriptions from the hatchery say they only lay three eggs a week. http://www.mypetchicken.com/chicken-breeds/Leghorn-Non-White-B66.aspx
	
		
			
		
		
	
				
			I would still not keep him, however--no matter how pretty. My brown Leghorn pullets didn't lay their first eggs until they were a full year old. I finally gave them away for free to a woman who had lost her flock. If you look them up, the brown variety of Leghorns is reputed to not lay nearly as well as their white cousins, so it's not just me. Even the descriptions from the hatchery say they only lay three eggs a week. http://www.mypetchicken.com/chicken-breeds/Leghorn-Non-White-B66.aspx
	