The Agenda view in Emacs's org-mode has similar ideas. In the week view you see great detail for the current day and a short overview of the days to come.
If you chose a state, say CA, a page that shows all the parks in California appears. The page is rather long and it takes some time to load. My browser actually wanted to stop the script. Maybe you can first show all the counties in CA and then the parks in a specific county.
Besides searching for a park near you, it might be interesting to search for a park near you that has a certain activity, say rock climbing.