[Basemap] Using a geotiff from seamless.usgs.gov as a background

As the subject states, I am trying to use a geotiff (shaded relief)
that I have downloaded from seamless.usgs.gov as the background in a
map. Mostly I am just confused about the seamless image projection and
bounds. The metadata defines the latitude of the top and bottom, and
longitude of the left and right sides. I assume that a mercator
projection is what I should use, but I am not sure. The bounds of the
image are also confusing, but they don't match the values specified in
the metadata or the values that I requested.

Any suggestions?