The quickest way to reason why bulbs/above heating is better.. Mats will not heat the air, so the second the snake leaves the mat/climbs off it will be subject to whatever temps the ambient is. Above lighting ensures controllable humidity, and a far better gradient of real penetrating heat from one side, gradually cooling the further away from the light/heat source you go
Nice Cali, I love the black and white desert phase. In the wild, all Cal kings use burrows or other cover where the microclimate is stable and slightly humid but mostly dry to the touch. When using a cage with a screen top, soil is a perfect substrate. Best of luck with the snake. Be sure to do a follow up!
