During his studies of New York streams, Horton determined that the degree to which rainfall could reach the aquifer depended on a certain property of the soil, which he called infiltration capacity.
He analyzed and separated the water cycle into the processes of infiltration, evaporation, interception, transpiration, overland flow, etc.
He believed these to include drainage density, channel slope, overland flow length, and other less important factors.
However, late in his career, he began to advocate a very different mechanism of "hydrophysical" geomorphology, which he believed better explained his prior observations.
Horton detailed his theory in a landmark paper published in 1945, only a month before his death, in the Bulletin of the Geological Society of America.
[1] A crowdfunding initiative was begun in 2023 via GoFundMe to recover Horton's published and unpublished works from the National Archive, which has received contributions from several hydrologists worldwide.