US, Canada, and Mexico 36km surrogates provided by Zac Adelman (UNC), 19 Jun 2017
Oil/gas "fromERG" surrogates originally from ERG at 4km, aggregated and shifted to 36US3 by Christos Efstathiou (CSRA), 6 Jun 2017

As of 19 Jun 2017, we do not have a gapfilled 801. For now, USA_801_FILL.txt is linked to NOFILL
so that we can use the same SRGDESC in SMOKE while we wait for gapfilled 801 to arrive.
