The 1990 Upland earthquake occurred at 15:43:37 local time on February 28 with a moment magnitude of 5.7 and a maximum Mercalli Intensity of VII (Very strong).

This left-lateral strike-slip earthquake occurred west of the San Andreas Fault System and injured thirty people, with total losses of $12.7 million.

Many strong motion instruments captured the event, with an unexpectedly high value seen on water tank near the epicentral area.

It was also felt in Ensenada, Baja California and it triggered 82 strong motion instruments at distances of 3–76 kilometers (1.9–47.2 mi).

[4] Rockslides left some roads closed in the San Gabriel Mountains and Pomona city hall was heavily damaged.