M3.1 earthquake 5km S of Ridgemark, CA

A magnitude 3.1 earthquake struck 5km S of Ridgemark, CA on Sat, Aug 21, 2021, 12:54 PM PDT (19:54 UTC), 9 km (6 mi) below the surface.

A larger quake followed: M4.0 6km NW of Pinnacles, CA. 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
3.1	ML, local (Richter)	Northern California Seismic System	Preferred · Final · ±0.169 · 58 stations
2.8	ML, local (Richter)	USGS National Earthquake Information Center	Reviewed · ±0.037 · 96 stations

17 people reported to the USGS what they felt; the strongest reported shaking was III, weak shaking.

Reviewed by a seismologist.

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

Within 100 km, magnitude 1.5 and up: 117 in the 60 days after this one and 59 in the 30 days before it.

The first 60 of 117.

From the USGS Earthquake Hazards Program and its partner networks, event nc73613006 (also filed as us6000f9e8). Read Sun, Oct 4, 2026, 5:33 PM UTC.