Here is the updated data (attached PDF) used for Figure 2 of Access Divided.
Source for state park data: National Association of State Park Directors. Annual Information Exchange Statistical Report of State Park Operations (NASPD AIX). 2014, (2012-2013 data).
Source for national park data: National Park Service, Visitor Use Statistics, Recreation Visitation By State and by Park for Year: 2015; https://fas.org/sgp/crs/misc/R42346.pdf