These Mexico 4km surrogates are consistent with those in:
/sol/work/EMIS/em_v6.3/ge_dat/gridding/surrogates/CONUS12_2010_CAN_MEX/

This is according to the header, which suggests those 12km Mexico surrogates
and these 4km Mexico surrogates were both developed in the Surrogate Tool
in June 2012.
