A Guy Called Tyketto writes:

Apparently you have never heard of shelving or floors.

I have, but that's irrelevant here. The chart is clearly marked, e.g.,

9999' MSL
=========
SURFACE

Surface means the ground. You can't go below an airspace that starts on the
ground.

All of that information is available on the Las Vegas
Sectional, which you would have realized if you looked at it, since
it's publically available.

I'm looking at the Grand Canyon chart, which is also publically available, and
is much more relevant to the Grand Canyon SFRA than any other chart.