Where do I start?

Where do I start to search? I have an older brother that was put up for adoption in 1964 in California. The only information that we have is; that it was a boy, and the adoption took place in California, we believe it would have been in the San Frisco area. We have medial information that we feel needs to be shared. Unfortunately, my Mom died of cancer, and no other family members are willing to share details of the adoption. Where do we go from here?