It was a relatively simple matter for John Carbutt to come to Minnehaha in the 1864-1866 period. He was in Chicago, and by 1865 there were trains between the Twin Cities and Chicago.
It took five days to travel to Minnesota from New York in the early 1870s. Probably it took another day to get from New Hampshire to New York. And perhaps French & Sawyer came out from Keene NH to the Great Northwest to photograph places like Minnehaha Falls. This photo is from the late 1860s (at a guess). Minnehaha was world-famous then, and fame was an inducement for photographers to visit here.