On March 18, 2002 I visited the courthouse in Downieville and checked the Sierra County CA birth, marriage and death record indexes. The Sierra County Clerk-Recorder has birth records from 1857, marriage records from 1852, and death records from 1864. The early vital records are incomplete (not everyone registered the event). I did not check the actual record but only the index, which is available for birth, marriages, deaths, and various other county records. I found the following:
BRISON / BIRSON None listed
McNUTT / NUTT None listed
Annie Sherman to Chas Scott (10/10/1906)
Morvie Sherman to Andrew Johnson (10/21/1896)
+ two additional in 1946 and 1962
I am not certain if any of these names are part of the family you are researching.
Further research: Other county records exist that you may wish to search. Deeds, naturalization records, mining claims, etc.