Speaking of rare earthquakes at 1,000 year dormant volcanoes, just a few days ago (May 31st), a different earthquake struck in South Utah at the Markagunt Volcanic Plateau (just before the Oregon Earthquake swarm struck off the West coast this week).
The Markagunt volcanic plateau also has been dormant for approximately 1,000 years.
Both long dormant volcanic areas have been hit by earthquakes in the past few days, which is certainly a sign of greater unrest in the region, and possibly a sign of another larger West Coast seismic event coming in the near term.
The earthquake swarm off the coast of Oregon is occurring directly on the flanks of a large undersea unnamed dormant volcano , thus these dormant volcanoes showing movement on the West coast are a sign of building stresses below the plate.
Information on this Arizona earthquake from the USGS: