RIDGECREST, Calif. (AP) — Large back-to-back earthquakes rattled some remote desert communities and put the rest of California on notice to be ready for a massive jolt in a big city. Scientists say a similar-sized quake in a major city like San Francisco or Los Angeles could collapse bridges, buildings and freeways, as well as spark devastating fires fueled by ruptured gas lines. No one was seriously injured in the quakes Thursday and Friday, which authorities attributed to the remote location in the Mojave Desert.