1861-62's flooding was definitely extremely northern stream driven. San Francisco had 24" of rain in January 1862 while we froze.
Bear in mind that month was about 8F colder here than January 1950 and over 12F colder than any 20th century January at Fort Walla Walla. Sacramento had significant snow at the valley floor, and the Sierras had insane amounts of snow with the occasional warm front to induce the rapid snowmelts when the southern stream energy poked its head in.
Probably not a situation that we will be repeating anytime soon.