As you head south on I-5 past Coalinga, the road runs just east of a long range of hills. From on high, and on the geologic map, the Kettleman Hills are a dramatic and obvious example of an anticlinal arch. The center is uplifted and dissected by erosion, so that the insides are the older rocks.
These hills drew the attention of oil drillers early on, but their holes came up dry until October 3rd, 1928, when a well struck a highly overpressured reservoir some 7000 feet down. A gusher resulted that lasted for three years. Oil production from the field was so great that the market was depressed and several other oil-producing states grumbled about the lack of regulation in California.
The town of Avenal arose with the oil boom, along with a host of businesses based on petroleum.
The classic geologic treatment of the Kettleman Hills oil field was issued in 1940 by the U.S. Geological Survey as Professional Paper 195.
Today the field is almost played out, although you can never discount new advances that might revive it. But the hills remain, blooming every spring. And the roadcuts, where you can access them, are still full of fossils.
You can cross the hills in three places, two of them busy highways: the Avenal cutoff in the north and state route 41 in the middle. I've tried looking for places to pull over on these roads and it basically shouldn't be done. Take the third way, farther south starting at the Utica Avenue exit; head west and then immediately south on 25th Avenue, taking it all the way to Twisselman Road and back to the freeway.
The edge of the hills is marked by the California Aqueduct, which is always worth contemplating.
There are a few roadcuts worth checking out. They all seem to be full of fossils dating from the Pleistocene, when the Central Valley was an arm of the sea. With the compression of the Coast Ranges, outlying folds in the crust of the San Joaquin Valley were pushed up into anticlines which formed traps for huge amounts of oil and gas.
Where Devil's Den Road splits off is the gap between the Middle and South Domes of the Kettleman Hills. East of there was the shoreline of Tulare Lake, an inland sea that was drained away long ago by the farms and cities of the Great Valley. Imagine the effect it must have had on the local climate here. This countryside, at its best, is worlds away from I-5.