Millions of Northern California residents received a Shake Alert warning at 8:06 am Thursday about an earthquake with an epicenter in Lyon County, Nevada, but the quake itself soon disappeared from the USGS website, and the agency said it was a false alarm.

An alarming "Drop, cover, hold on" message popped onto the phones of Bay Area residents this morning with the MyShake app or other warning system, warning of imminent shaking from a large earthquake in Nevada, centered near Dayton — which is 29 miles south of Reno, and about 12 miles east of Carson City. But now it looks like that was all just a false alarm.

The US Geological Survey posted to Xitter at 8:45 am apologizing for the alert, saying, "There was no M5.9 earthquake near Carson City, NV. We are currently looking into why the alerts were issued."

Subsequently, the USGS-managed Shake Alert system posted a message saying the incident was being investigated, and added, "This system has delivered more than 170 real alerts since 2019 and this incident is both unprecedented and rare."

Was the USGS hacked? Did somebody's truck drive over an earthquake sensor in the desert?

We may know more soon. Angie Lux, a scientist at the Berkeley Seismological Laboratory, which manages the MyShake app, tells the Chronicle, "It’s gonna take a little bit of time to understand exactly what happened with the system, but we can say that there was no earthquake and that we’re looking into what happened."

And maybe this is just me, but it also seems like the MyShake messaging was kind of extreme for an earthquake that happened hundreds of miles away, which was likely only to cause minor shaking in the Bay Area, if any at all?

This is a developing story and has been updated.