the files at webgis say spatial res 30 30 1, seems there is better by comparison
of the two Grand Canyon files,

3 arc seconds 90 meters World-wide SRTM
1 arc second 30 meters DEM from topo, USA SRTM
1/3 arc second 10 meters DEM from topo
1/9 arc second 3.4 meters Newer DEM from LIDAR

included Grand Canyon said,
[15] spatial resolution:   3 3 1

and all that leaves speculation room for spatial speculation.

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