250 miles is not close enough to feel a 6.4 *in California*. In the Midwest, when the New Madrid fault slips, even a magnitude 4 quake can be felt for 400+ miles. The land out there is more or less one solid piece, while California is made up of thousands of smaller pieces all scraped off the Pacific plate as it subducts under the North American plate. So it damps out the vibrations a lot faster than in the Midwest.