The first trees planted in California (specifically, San Diego) were olive trees. The Mission padres used olive oil as lamp oil and for the sacrament of anointing the sick.

It should be noted that olive oil was one of the first ingredients to dominate the original California cuisine. In the beginning, settlers didn't have enough cattle for suet or enough pigs for lard but they had olive oil.

Availability may have determined the Californian affinity for olive oil as opposed to the Mexican affinity for lard. It gained an early foothold before people who preferred butter moved to California