In the early morning of Wednesday, April 20, an earthquake, magnitude 2.9, occurred about 2 to 3 miles west of Little Thomas Mountain and the same distance south of Baldy Mountain.
The quake was at about 4:40 a.m. During the next 12 minutes, another four minor quakes were recorded. Their magnitudes ranged from 0.3 to 1.7. About an hour later, a 0.5 shake was recorded about 10 miles southeast of the original in the Santa Rosa Mountains area.
During the next five days, nearly 25 more and smaller tremors occurred. The largest of these was a 1.4 magnitude and occurred Saturday morning. The largest cluster was south of the Santa Rosa Indian Reservation, and another cluster occurred along Rouse Ridge.
The initial report of the April 20 quake, minutes after it occurred, measured the trembler at magnitude 3.3, but the current U.S. Geological Survey data indicates it was 2.9 magnitude.