Summary

The information and inferences therefrom concerning central California earthquakes reported as occurring in the 1830's, according to the conclusions reached in the foregoing discussion, may be summarized as follows.

1836—April 25, 5 a.m. A “strong” shock. Monterey. This may possibly be a foreshock of the June 10 earthquake. If so, it must have been felt at points around the Bay of San Francisco, but no reports are available.

1836—June 9, about 4 p.m. Monterey. Described as strong and short by Gomez; strong, and of about a half minute's duration, by Vallejo. It is probably a foreshock of the earthquake of the next morning, but no reports are available from other localities.

1836—June 10, 7:30 a.m. X. East of San Francisco Bay. An earthquake of great intensity comparable with and possibly stronger than that of October 21, 1868. Large fissures were formed and “innumerable” aftershocks occurred, decreasing in violence, but “continuous” for a month. The account stresses the effects along the foothill belt from San Pablo to Mission San Jose, which indicates an origin in the Haywards fault. The fissures were probably, at least in part, fault-trace phenomena. Reported by Gomez in Monterey as of more violence and duration than the shock of June 9. Described by Vallejo as strong, lasting close to a minute in Monterey, causing havoc in Monterey and Santa Clara, and arousing great fear among the people. Intensity apparently at least VII at Monterey and Mission Carmel.

1838—Late in June, just after noon. X. Comparable with the earthquake of April 18, 1906. Originated in the San Andreas fault, and violent fault-trace phenomena described by Charles Brown as observed in the hills behind Palo Alto near the present Searsville Lake: a great fissure which he describes as ten to twelve feet wide and running from near San Francisco to the latitude of of Santa Clara; the ground cracked in all directions; thousands of trees broken off; water thrown from creek bed; adobe walls cracked. Violent at Yerba Buena (San Francisco), walls cracked at Presidio, a sand hill bodily shifted (according to Spear); house shaken down at San Jose (town), and walls badly injured at the San Francisco, Santa Clara, and San Jose missions (Captain Paty); crockery and glassware broken, walls of adobe buildings cracked, inhabitants “frightened out of their wits” in Monterey (Major Warren). Captain Paty reported aftershocks as “frequent since” (his ship left the coast September 19, 1838). The fault rupture may have occurred throughout all or most of the line active in 1906, but north and south beyond the limits indicated by Brown it lay under water or in wild country uninhabited by whites (except at Fort Ross, from which we have no report). The evidence of greater intensity at Monterey than in 1906 may mean that the fault rupture extended farther south in 1838 than in 1906.

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