The 1988 Upland earthquake caused minor damage in the epicentral area, but would have been of relatively little note were it not for the possibility that it may have been triggered by the Whittier Narrows earthquake -- 9 months earlier, and 20 km away. While poorly understood, these kinds of causal connections are of great interest as they apply to the potential of more accurately forecasting earthquake probabilities. There is no conclusive evidence, however, that shows that the 1988 Upland earthquake was triggered by the Whittier Narrows earthquake; the relation between the two is likely coincidental.

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The 1990 Upland earthquake was much more damaging than the quake of 1988. It triggered landslides which blocked roads in the Mount Baldy area, and it caused some damage to the San Antonio Dam, which lies across the path of the main watershed coming south from Mount Baldy. Thirty-eight people sustained minor injuries, and damage was considerable near the epicenter. The quake was felt as far away, northeast, as Las Vegas, Nevada, and as far south as Ensenada, Mexico.


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