The northern part of the San Andreas fault, some 300 kilometers long, ruptured from end to end on 18 April 1906, producing an earthquake of approximately magnitude 7.8. For several decades afterward, very little seismic activity occurred along this stretch, which reaches from Shelter Cove southeastward to San Juan Bautista. However, earthquakes have been increasing roughly since the 1980s, a period that includes the 17 October 1989 Loma Prieta event, of magnitude 7.1, in the San Francisco Bay area. While moderate and large earthquakes like 1989's are of concern and can cause deaths and damage, another great event the size of the 1906 quake is not anticipated for at least a century.
This tour of the San Andreas fault begins at the north end. The next part of the fault, beyond San Juan Bautista, is the creeping section.
- Index Map of the Northern San Andreas FaultLay of the land
- Mouth of Alder CreekWhere it all begins
- Fault Trace at Alder CreekMarks of movement
- Deflection of Alder CreekA common phenomenon
- Shutter Ridge at Alder CreekMoving the goalpost
- San Andreas Fault North of Skaggs Springs RoadBig ditch in the deep woods
- Rocks of the Gualala BlockDistinctive sandstones
- San Andreas Fault at Fort Ross RoadSigns of movement
- Sag Pond in Fort Ross OrchardA secret wet spot
- Fault Trace South of Fort RossA rumpled hillside
- Abandoned Course of Mill GulchHigh and dry
- Fault Trace at Mill GulchView to an offset
- Graphic Index
- Text Index
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