Depends on the school.
For the 2014 entering class:
University of Michigan had 52.6% of it's students from out of state.
UC Davis had 2.9% of it's students from out of state.
The MSAR has this data under the "Acceptance Information" tab for each school.
Generally, higher ranked public schools are more open to out-of-state applicants.
UCSF (Rank 4): 17.6% OOS
UCLA (Rank 12): 11.9% OOS
UC Davis (Rank 40): 2.9% OOS
Also, high-ranked non-California public schools are more OOS friendly than high-ranked California schools
University of Washington (Rank 10): 48.9% OOS
University of Michigan (Rank 12): 52.6% OOS
(Percentages are calculated from 2014 MSAR data, and rankings are US News Research rankings.)
Also, most private schools (Harvard, Stanford, University of Chicago, Columbia, Cornell etc.) have no in-state bias. There are exceptions, like Mercer in Georgia, and Baylor in Texas.