I keep stumbling across more references to early legit and musical venues up and down Main Street.
The Main Street Theatres page continues to grow with added listings of early legit theatres on Main and nearby. The 1958 adobe venue Stearn's Hall, the 1886 Mott's Hall (where Charles Dickens once appeared) and the 1876 Wood's Opera House now have at least the beginnings of their history on the page. Information is scarce -- and sometimes contradictory. Let me know if you have anything to add!
On Los Angeles St., Sanchez Hall was another early "theatre" if that is even the right word, opening around 1841.
Two better known Main Street legit theatres, the 1893 Burbank Theatre (548 S. Main), and the 1884 Grand Opera House (110 S. Main) now have some stage specifications added to their pages.
The photo at the top of this post is a circa 1905 view of the Burbank by Martin Berhman from the California State Library. On their website: full size view