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San Onofre State Beach, California, United States

San Onofre Trail 3 to the Cristianitos Fault

A moderate beach hike along a geologically significant area in San Onofre State Beach, visting the Cristianitos fault.

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Difficulty: Moderate
Length: 3.8 miles / 6.1 km
Duration: 1-3 hours
Overview: The Cristianitos Fault is a major earthquake fault line located less than one mile from the San Onofre nuclear power plant. This hike takes you on a 3.8 mile loop through San Onofre State Beach to the site of the fault line. Along the way, you’ll see the Monterey Formation, which holds most of the oil and gas deposits known in the LA basin and off the coast, as well as the abrupt end of the San Mateo formation at the fault line.

Tips: Day use parking at San Onofre State Beach is $15 or you can use your annual day use parking pass.

The beach has stretches that are completely covered with cobblestones. Shoes with good ankle support would be advisable.

There isn't much shade, so bring a hat and wear sunscreen.

There are restrooms and water along the bluff campgrounds, but none on the beach. Bring water.

The bluffs are unstable and dangerous. Stay on marked trails.

Points of Interest



You can park in any unnumbered space along the bluffs. The numbered are reserved for camping.

For this hike, park near Trail 3.

Turn right down Trail 3

Trail 3 is one of six trails leading down to the beach from the bluffs.

Watch your footing on the downhill sections. The loose gravel can make it hazardous.

USGS Benchmark

Look for this USGS benchmark at the final turn before reaching the beach.

Monterey Formation

Here you can see a section of the Monterey Formation exposed. This shale formation contains most of the oil and gas deposits in the LA basin. The oil platforms off the coast of Southern California drill down into this formation.

It's exposed here because of the activity on the Cristianitos Fault.

The Cristianitos Fault

The Cristianitos Fault is easily found. The bluff to the north is identified by the wide light-colored band known as the San Mateo Formation. This band abruptly ends here.

Scramble 10-15 yards up this hill and see the strike plate of the Cristianitos Fault.

The layer of rubble above the San Mateo Formation, as well as the alluvial material above that, has been undisturbed. Geologists have dated that material to be 125,000 years old, so we know that the fault has not been active for at least 125,000 years.

This is why there were able to build the San Onofre nuclear plant less about a mile away from the fault line -- the fault is essentially "dead."

When you finish exploring the fault, head back south down the beach, retracing your steps.

Trail 1

Heading back, take Trail 1 up to the bluff and experience this area from a different perspective.

Stay right

The spur to the right leads to another parking area. Stick to right on the main trail here.

Bluff Trail

At the top of the bluff you have two options. You can walk along the pavement and the campsites, or follow this dirt trail which extends along much (but not all) of the bluff.

Take a right here the nicer bluff trail back to your car.



Trail 2

An alternative route to the beach. If you want to shorten this trip, start here instead of Trail 3.




These are typical of the bluff campsites. There aren't very rustic, especially given their proximity to the freeway, but they all include a fire ring and picnic table, and you are a short hike from the beach.


Pictures in this guide taken by: jeffhester, arellano21

San Onofre Trail 3 to the Cristianitos Fault Trail Map

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