The interesting thing is that no one knows what California looked like BEFORE the Spanish arrived.
Recent research suggests there were only shrubs and lily-like plants; the wild flowers and grasslands, which predominate today, may have been present, but only in small patches:
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the invasion of California by Mediterranean grasses and forbs beginning in 1768 has been one of the most dramatic, yet remarkably undocumented, ecological shifts. Very little is known about pre-Columbian vegetation cover on land now characterized as California grasslands....examinations of historical accounts have cast doubt on the assumption that native grasses dominated California's prehistoric prairies. The earliest European explorers’ accounts of vegetation in the Central Valley are sparse and lack species-level detail, but generally suggest either an abundance of flowering broad-leaf plants (forbs) or bare ground....