Petrolia, California. One of the most beautiful places in the state. A hidden gem virtually undeveloped. Petrolia is about 50 miles south of Eureka, CA located in Mattole Valley, part of the "Lost Coast" region. Getting there is half the fun...twisty mountain roads lead to a lush green valley. Petrolia is so isolated (it has a population of about 300-500 people) that few tourists visit. But it's worth the trip. The city gets its name from being the first site where oil was drilled in CA.