M3.6 earthquake 6 km NE of Ridgemark, California

A magnitude 3.6 earthquake struck 6 km NE of Ridgemark, California on Tue, Aug 7, 1990, 11:39 AM PDT (18:39 UTC), 7 km (4 mi) below the surface.

A larger quake followed: M4.4 14 km S of Tres Pinos, California. This one was a foreshock.

Map

Where this earthquake was located, with the others nearby. Select one for its page.

Different scales measure different things and differ by a few tenths. The USGS marks one as preferred, and it is the one this page uses.

Mag.	Scale	Computed by	Notes
3.6	ML, local (Richter)	Northern California Seismic System	Preferred · Final · 0 stations
3.6	ML, local (Richter)	USGS National Earthquake Information Center	Reviewed

The USGS’s account of the effects of this earthquake.

Felt (III) at Aromas. Also felt at Moss Landing.

From the USGS event page for nc20091966. U.S. Geological Survey text and figures are in the public domain.

No one has reported feeling this quake to the USGS.

Reviewed by a seismologist.

Distance and direction from each place to the epicenter, with its forecast.

Within 100 km, magnitude 1.5 and up: 182 in the 60 days after this one and 102 in the 30 days before it.

The first 60 of 182.

From the USGS Earthquake Hazards Program and its partner networks, event nc20091966 (also filed as usp0004d2w). Read Sat, Oct 3, 2026, 1:10 PM UTC.