M3.0 earthquake 8km SSW of Rio Dell, CA

A magnitude 3.0 earthquake struck 8km SSW of Rio Dell, CA on Mon, Dec 20, 2021, 1:06 PM PST (21:06 UTC), 27 km (17 mi) below the surface.

A larger quake followed: M4.6 50km W of Petrolia, 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
3.02	ML, local (Richter)	Northern California Seismic System	Preferred · Final · ±0.323 · 19 stations
3.0	ML, local (Richter)	USGS National Earthquake Information Center	Reviewed · ±0.038 · 92 stations

1 person reported to the USGS what they felt; the strongest reported shaking was IV, light 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: at least 199 in the 60 days after this one and 64 in the 30 days before it.

The first 60 of at least 199.

From the USGS Earthquake Hazards Program and its partner networks, event nc73666396 (also filed as us6000gdyt). Read Sun, Oct 4, 2026, 12:42 PM UTC.