The magnitude 5.5 quake occurred at 3:43 p.m., Wednesday, February 28, 1990, lasting thirty seconds. There was a 3.6 foreshock at 12:37 p.m., and over 30 aftershocks in the next week.  Initially billed “the Upland Earthquake,” the classic left-lateral strike-slip quake was finally determined to be centered just barely inside the northern Claremont city limits, four miles under the corner of Deep Springs Drive and Grand Avenue. The quake moved Claremont just a little closer to Big Bear, and moved Mt. Baldy a little closer to Los Angeles. In Claremont, the most common structural damage was to older stone chimneys, with more than a hundred reported to have lost some of their stones.

Damage to the campus included minor cuts and bruises, a few broken windows and glassware, lots of fallen ceiling tiles, some broken water pipes, and a few building cracks. The Scripps 42nd annual ceramics show lost nine of the fifty-four works on display. And all over the campuses, offices and libraries were knee-deep in books.

At Honnold/Mudd the new Multi-Tier Stack, designed to withstand considerable movement, came through the quake beautifully, with only minor plaster damage where it bumped against the Mudd building. Elsewhere in the library, stacks were tilted in a few areas, and everywhere thousands of books were down. As soon as the building was declared safe and all the stack bracing checked and improved, the staff began the task of picking up the books and putting them back in order. A store simply sweeps up the broken items and reopens, sometimes only hours after a quake. A library takes longer, and the students were very understanding of the four-day closure, especially when pictures of aisles completely blocked by books were posted on the doors.

About a thousand hours of staff time were spent picking up between 100,000 and 200,000 books, and by 8 a.m. Monday, Honnold/Mudd was reopened. The art folio stacks took a little longer since bent stacks had to be replaced, and books stayed piled against the wall for some time. No one in the building was injured.