You can do it on the USGS site, at least for other rivers. I usually google "flows" for whatever river I'm looking at, near the top of the page there is a spot for the date, set the start and end date for the time frame you want to look at.
So for instance, San Juan, April 2015, set April 1st for the start date, and April 30th for the end date, and you will get the historical data for that time frame instead of the current data.
Took me forever to figure that one out if it makes ya feel any better!
" I wish I were a headlight, on a North bound train..."