The Mission Santa Cruz was located acorss the street from the home of Don Rafael Castro. I found several of his children, or rather records of them at Parejo church in Watsonville, ie, marriage and baptismal records. Could your Salvador be related? There might also be funeral records there, or you might try the diocese at monterey, they keep archives of several old missions. I believe Don Rafel may have been married at the Mission, but apparently the mission closed or something because they all showed up in Watsonville. It's worth a try anyway.