Not all oil companies claim to see much potential. Chevron, which has been pumping oil conventionally in the area for over a century, told CNBC in a statement, "Chevron does not see the same level of promise in the Monterey Shale as other companies...we have not been encouraged by the results of the wells we have drilled into the formation."
(Read More: Oil May Extend Losses If Fed Minutes Hint at Policy Pause)
Then there are the concerns some in the state have about fracking in an area near earthquake faultlines and other environmental issues.
"California has no regulations particular to fracking," said Nathan Matthews, associate attorney with the Sierra Club. His organization is suing the state, claiming California is not enforcing existing regulations, and it's asking for a moratorium on all exploration of the Shale until California finalizes rules for hydraulic fracturing. "That oil's not going anywhere," said Matthews. "There's isn't a huge harm in just waiting to make sure we understand what we're getting into."
What are the chances any of this exploration will pay off?
(Read More: Senate Examines Implications of Shale Revolution)
"I don't really know what the break point is for the companies," said Tupper Hull of the petroleum association. "That's what our members are trying to figure out right now."
John Lehn said if he was trying to predict what inning the industry's in In the game of extracting oil. "We're probably in the recruitment phase," he said.
Looking at a test well owned by California-based Aera in Kettleman City, Lehn explained, "These folks that are out early want to be as quiet as they can, secure as much land or the mineral rights as they possibly can before the information gets out to the others. But you're here, so it's not much of a secret, right?"
—By CNBC's Jane Wells; Follow her on Twitter: @janewells
CORRECTION: An earlier version of this story mistakenly identified Aera as based in Canada. California-based Aera Energy is a privately held limited liability company and is not affiliated with the Canadian firm by the same name.