463,000 bopd (2018) Puts California in seventh place among the oil producing States,a bit of a slide in the past few years in the rankings (a combination of more production elsewhere, and less in California). That does not include the midstream/downstream part of the industry, nor Natural Gas. (Midstream is the pipeline, transportation, and processing part, downstream is the wholesale/retail of refined products. All involve transportation, and jobs range from truck driver delivering to your local gas station to the propane bottles for your barbecue grille to roughnecks and drill bits. There are a tremendous number of service companies involved in the oil industry, and with all the various (and to many of us, unusual) requirements placed on the industry in California, the amount of revenue generated in all aspects could be huge. They do not enjoy a geological situation conducive to horizontal drilling and hydraulic fracturing that many of the mid continent basins enjoy, so they have to work a little harder for the oil and gas there, which means more wells, and that translates to more service company involvement, and greater related revenues.
For instance, in North Dakota, a typical Bakken/Three Forks production pad will have eight wells drilled on a 1280 acre spacing (Two square miles), each with about 9500 ft. of producing wellbore in the target formation, usually four wells in the Middle Bakken and four in the Three Forks. That means there are some 76,000 ft. of wellbore in producing intervals, to be hydraulically fractured, and the results have shown initial production rates of as high as over 10,000 barrels of oil per day, from just one well. (The average is something over 1,000 BOPD).
In a vertical well, it is an unusually good formation that will have productive intervals over 100 ft, and it would take 760 wells to match one well pad in ND if that is the case. Because of that, imagine moving the rig to drill each of those 760 wells, to different and unique locations, with all the earthwork and access road construction, and eventually gathering infrastructure needed to collect the produced oil and store it for transport.
What we noticed in North Dakota, was that with the advent of pad wells and walking rigs (which move by themselves from wellbore to wellbore on the pad without having to be dismantled and rigged up on the next wellhead) the amount of service company revenue for rig movers and earth construction diminished considerably (with 4 wells the new norm before a rig move was needed, 75% of the rig moving market went away). Similarly, the costs/revenues from constructing drilling locations dropped, and gathering infrastructure was simplified, with a single road for access, pipeline hookups simplified, etc. With advancements in drilling technology, the time needed to drill a well was reduced significantly as well. (Yes, we were/are blessed, and we know it, but one man's blessing requires significant adjustments for another). So, to make an already long story shorter, the service company revenues fell overall in many areas, here.
As to whether the numbers seem credible, across all areas of the industry and related revenues. I can't say for California, but there is a great deal more to the industry and the number of offshoot jobs that accompany it than just a drilling rig or a frac crew and a few truck drivers.