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These fields likely formed from the subduction of a spreading ridge on the Farallon tectonic plate, allowing hot material to pop up through the coastal mountains and erupting in fits and starts. Many cycles of explosive and effusive rhyolitic eruptions built up the Pinnacles in their original location, just to the north of Santa Clarita, CA. 

But the Pinnacles aren't anywhere near Southern California now - so what happened? 

That's the next part of the story. As the Farallon tectonic plate was completely subducted beneath the North American plate, tectonic movement switched from plates colliding to plates sliding past each other - a transform boundary. This was the famous San Andreas fault zone, and as it split the coastal mountains, it also dragged most of the Pinnacles volcanic rocks northward on its west side. The remaining bits are still located in Southern California and are known as the Neenach Volcanic Formation, but the rest moved 195 miles (315 km) northward to their current location 30 miles (48 km) southeast of Salinas.

Along the way, thousands of feet of rubble covered and then were eroded off the volcanic rocks, and even the intrusive rhyolites were exposed to weathering. Over time, the softer breccias were worn away into tall spires and hollowed out into caves, still perched atop the more resistant lavas and intrusions. Nowadays, these fantastic formations make up one of the newest National Parks, and are also home to a thriving population of California Condors!

Read more about the geology of Pinnacles in https://pubs.usgs.gov/of/1987/0135/report.pdf