There probably were Chinese in Marysville from 1849 - Marysville was the last stop on the ferry from San Francisco to
the gold country so most of the miners (including the Chinese) took the ferry to Marysville then headed to the mines on horses or walked.
There was a Marysville flood in 1853 and then a flood every decade or two. The 1861/62 flood was most devastation that effected the entire region:
"The Folsom Telegraph thinks that those journalists who have centered many of their energies against Chinese immigration
ought to be shocked at the superiority of water over their spirit in decreasing the 'Chinese nuisance,'" the paper joked,
"for it is not to be doubted that two or three thousand Chinamen have perished in California since the commencement of the present rainy season."
Flood report published in 1931: how many Chinese were drowned near Marysville CA?