Measured on a seismic scale that is based on an isoseismal map or the event's felt area, the 6.4 Mla and 6.2 Mla  events were assigned a maximum Mercalli intensity of IX (Violent), and affected the North Bay and Central Valley areas.

The primary tectonic feature of the region is the strike-slip San Andreas system of faults (that move laterally alongside one another).

The furthest extent that they were felt was from Redding in the north to Salinas and Fresno in the south and to Virginia City, Nevada in the east.

Observations of the range front and modelling of strong ground motions led to the presentation of a 17 km (11 mi) rupture on the west-dipping Gordon Valley blind thrust fault that could have produced the felt intensities that were specific to the April 19 event.

Damage also occurred at Dixon as well as the area of the highest reported intensity of IX (Violent), midway between Winters and Vacaville, at Allendale.

No locations in Napa county reached any higher than intensity VI (Strong), indicating that the shock originated east of the Vaca Mountains.