How far is it between the lowest point and the highest points in the continental US?

Both the highest and lowest elevations in the continental United States lie in California.

The distance between them (as the crow flies) is just under 88 miles (142 kilometers).

The highest elevation is Mount Whitney (14,505 feet/4,421 meters above sea level) in the Sierra Nevada range.

The lowest elevation lies in Death Valley's Badwater Basin (-279 feet/-85 meters below sea level).

https://wiki2.org/en/List_of_extreme_points_of_the_United_States+Newton

Plugging in the GPS coordinates from the source in psnz's answer, I ended up getting 135.7km or 84.3 miles (the same in two online distance calculators).

Taking this, I thought it would be interesting to see how the distance changes if instead of as the crow flies, we accounted for the slant the line would take it we connected the peak of Mt Whitney to the lowest point in Badwater Basin. A simple application of the Pythagorean theorem using 135.7km as the base and 4.506km as the vertical distance between the high and low points gives us 135.8km (to 4 significant figures). So an extra 100m if you wanted to actually travel the minimum distance between the two points (though I suspect that line probably intersects with the ground at some point so it wouldn't be physically possible for a mere human anyway - though something like a neutrino would have no trouble!).

I know usage varies, but at least some people (and the USGS) acknowledge that Alaska is on the same continent as the contiguous 48 states, in which case the highest point at Denali (Mount McKinley) is much further away than Mount Whitney from the lowest point in Death Valley. The distance between those points is calculated by https://www.calcmaps.com/map-distance/ as about 3779 km or 2348 mi.

sportsherald is right. The Continental United States (CONUS) includes 49 of the 50 states plus the District of Columbia. So only Hawaii is not part of the CONUS. The contiguous United States (officially the "Conterminous United States") does not include Alaska, Hawaii, or any other territories under the control of the United States.

https://simple.wikipedia.org/wiki/Continental_United_States