Gibb, my earliest source is from ONCE A WEEK, "On Shanties", August 1, 1868, p. 92:

"Blow, boys, blow, for California, O,
There's plenty of gold in the land, I'm told,
    On the banks of the Sacramento."

http://books.google.com/books?id=8dRMAAAAMAAJ&pg=PA92-IA4&dq=%22So+blow,+boys,+blow,+for+Californio%22&lr=&cd=12#v=onepage&q&f=f

I've not found anything else until later.