Map: San Andreas Fault Zone



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Map: San Andreas Fault Zone 

 

During the 25 million years that the San Andreas Fault has been active, most of the fault movement has occurred within a zone that is about half a mile wide. At the Hot Spot, the fault zone 

extends from the upper part of River Beach Road to the opposite side of the Gualala River. The rocks within fault zone have been broken, crushed and offset many times along many differ-

ent fault traces. One of the best places to see many of the fault features is on the short San Andreas Fault Interpretive Trail , To get to the trailhead go down River Beach Road and take the 

one-way Hot Spot Loop Road. Continue past the Hot Spot and park in the small parking area near the end of the loop. The trailhead is on River Beach Road just uphill from the parking 

area.  


San Andreas Fault 

Interpretive Trail 

Hot Spot 

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Parking 



Hot Spot Loop Road 

A GEOLOGIC TRIP  

to the 

SAN ANDREAS FAULT 


Photo: Looking northwest down the Gualala River  

from the Hot Spot

 

The Hot Spot is on the Gualala River and is a popular destination 

for summer swimming when the river is slow and the water is 

warm. The Hot Spot lies within the San Andreas Fault zone, and a 

visit to the Hot Spot provides a good opportunity to see some of the 

features of the San Andreas Fault. 

  

Gualala River 

Hot Spot 



Gualala 

Gualala River 

Pacific Ocean 

 Offset of the Gualala River

 

by the San Andreas Fault 

 

During the last 500,000 years the San An-



dreas Fault has moved the mouth of the 

Gualala River seven miles to the northwest 

and the river has followed the fault zone to 

stay connected with its mouth.  



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1 Mile 


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Hot Spot 




Photo: Trailhead  

The trailhead for the San Andreas Fault trail is on River Beach Road just uphill from the beginning of the one-way Hot Spot Loop Road. One hundred years ago this part of the Gualala 

River Valley was the site of and extensive redwood logging operation, and  the trail also offers a good look at how the logging operation was carried out.  

San Andreas Fault Interpretive Trail 

Trailhead 



Photo: Pamphlet Box near trailhead 

Trail guides are available at the pamphlet box near the trailhead. Redwood forest, logged, scars of logging 



San Andreas Fault Interpretive Trail 

Logging 

Notches for springboards used for logging 


Photo: Looking northwest along trail

 

The first part of the trail follows along the top of a northwest-trending 

ridge. This is one of several ridges that have formed within the fault 

zone. Ridges like this are a common feature of faults like the San An-

dreas and are formed when the rocks in the fault zone are squeezed 

and/or uplifted by the faulting.  

 

 

San Andreas Fault Interpretive Trail 



Ridge 


Sag Pond 

Photo: Looking  from top of ridge to sag pond on west side of ridge 

 

Sag ponds such as this are also a common feature of the San Andreas Fault zone. They are formed in the low spots between the ridges and/or when stream drainage is offset and blocked 

by horizontal movement within the fault zone. The water does not drain from the sag ponds because the rocks in the fault zone have been ground to a fine clay and are impermeable.  

San Andreas Fault Interpretive Trail 

Sag Pond 



San Andreas Fault  

Interpretive Trail 

Tree Damage 

Photo: Double Trunk  

During the 1906 earthquake a number of trees were damaged by the severe 

shaking, either breaking off the top or splitting the trunk, When this happens, 

a double trunk often develops above the damaged area.  




San Andreas Fault Interpretive Trail 

Fault Scarp 

Photo: Looking southeast along Hot Spot Loop Trail 

The end of the San Andreas Fault Interpretive Trail connects to the Hot Spot Loop Trail and the loop trail returns to River Beach Road. On the return trip, you pass a fault scarp that formed 



during uplift of the ridge on the left side of the photograph.  

Fault scarp 

Ridge 

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