This branch left the Southern Pacific line (which ran from Goshen Junction to Coalinga) at Armona at the site of the SP's Armona passenger station. From there it proceeded northwest to Riverdale.
This line was abandoned in 1951, with the rails being pulled up sometime between 1952 and 1960. The former Armona passenger station was converted into a lumber store sometime in the late 50s or early 60s.
Thanks to Danny Pearce for contributing information about this route.