From the Guidebook:
The historic Capitol was
designed by architects M. F. Butler and Ruben Clark. Its
style is an adaptation of Roman Corinthian architecture.
Work began in 1860 and by late 1869 the Capitol was partly
occupied. In 1874, construction ended at a cost of $2.45
million. The west wing which once housed all branches
of government is now a legislative facility. Its design
and construction are tributes to California's pioneer
architects, craftsmen, and builders.