From the Document: "Like other federal agencies, the National Park Service (NPS) has halted most operations during occasional government shutdowns resulting from lapses in appropriations. Over the past 25 years, such shutdowns occurred in late 1995/early 1996, October 2013, early 2018, and, most recently, from December 22, 2018, to January 25, 2019. Although government shutdowns have affected many agencies and programs, public and congressional attention has focused particularly on certain impacts, one of which is the effect of a shutdown on the National Park System."
CRS In Focus, IF11079
Congressional Research Service: https://crsreports.congress.gov/