According to "Historic Highway Bridges of California", 1990 by Cal Department of Trans., the bridge was built in 1899. It is one of four remaining Phoenix Bridge Company bridges in California. No mention is made of the bridge being a relocation project (see page 167). See also pp 48 thru 53.
Definitely an 1870's-1880's span, and a beauty at that! Phoenix columns on the endposts, top chords, and main verticals. I also have heard of bridges from the East being replaced with newer spans and the old span dismantled and relocated far away. "Go West young man.....and take the bridge with you!".
This bridge is probably one of the many recycled truss bridges on the west coast. I have seen many old trusses that have been moved to the west coast from the Midwest that date from the mid to late 1800's, but have construction dates in the 1930ís and 1940ís.
As roads and railroads were improved in the more populous regions east of the Rocky Mountains, areas of the Pacific Coast were just developing there roadways. So, many structures were torn down and moved west.
I will go out on a limb here and suggest that this brige was built well before 1940. I would suspect 1870s, given the columns and portal bracing. This bridge is definitely a great find!