The Sierra Pacific I know was based at OAK
Flew Beech 18s.
Started service 11Nov1965 on the Oakland-Lake Tahoe-Reno route.
For a short time they had an interline agreement with Western Airlines.
Service however ended in 1966.
As far as I know, there is no connection with the carrier of the same name that was formed in 1972 at Burbank.
This airline actually began as Trans-Sierra Airlines (XS) in 1971 with a fleet of Piper Navajoes, Cessna 402s, and Convair 340s.
Trans-Sierra flew to Los Angeles, San Jose, Burbank, Bishop, and Mammoth.
After the reorganization in 1972, the new name (Sierra Pacific) brought with it a new code, SZ
, and a revised network; San Jose was dropped, Fresno was added.
They were around til 1979 as a scheduled carrier...which can mean many things......