Abbreviations, periods, definitions, and sources of nature variables used in this paper.
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aData exists for 1975–1981, but we were advised by BLM (T. McDonald, pers. comm.) that while 1982 and later data were based on reported use at fee sites and recreation concessions, data prior to 1982 was not and was much less reliable.
bBLM data does not exist for the four years 1990 and 1993–1995: this is not our omission.
cWeighted by survey firm to best estimate demographics of US population.
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2013-02-21
