Mt Whitney Zone Forums General Discussion What's the real elevation of Mt. Whitney?

I just ran VERTCON myself and found the datum conversion to be +6.13 ft going from the old retired datum NGVD29 to the current datum NAVD88. This is key information and it would be helpful if these NGS data sheets indicated the datum differential, but I don't see it. They do a geoid height adjustment, but that's more complicated to understand.

So just converting from the old datum (NGVD29) to the new datum (NAVD88) increases the original elevation by +6.13 ft. That datum shift is pretty much the same for every elevation point in the general area. That explains most of the confusion about how the elevation suddenly went up so much. But it doesn't explain the various new elevations that are popping up. The other confusion comes from deciding which elevation to convert? That's the historical part of the problem. Various elevations are stated from various surveys. Which one is best?

There are two NGS DATASHEETS for Mt. Whitney (maybe more) GT1810 and GT1811. GT1811 seems better to me. For one, it appears to be more recent, based on the numbering scheme. But more importantly, GT1811 is based on converting a previous survey control to the new datum. In contrast, GT1810 scales the height from surrounding benchmarks used to develop the 1994 topo Quad Mt Whitney. The quality of converting a single good survey benchmark (GT1811) should be better than interpolating from topo data (GT1810).

There are two important survey monuments used for GT1811 DATASHEET, one located on a rock stamped 14502. The rock is 3.5 ft tall. This monument is apparently the highest point that we're interested in. But the best horizontal control on the summit seems to be the Whitney 1950 monument (above 10 ft north of 14502). GT1811 adjusts horizontally from Whitney 1950 and Monument 14502 to improve the horizontal control, but that doesn't really affect the elevation at 14502.

If you add 6.13 ft to 14502 you get 14508 ft NAVD88. If you subtract the height of the rock, you get 14505 ft. The rock height could be an explanation for the difference between 14508 and 14505. It seems reasonable to think interpolation could miss a boulder, but that's just speculation.

There are other elevations to convert, just to add to the confusion. The National Park Service 1930 plaque puts it at 14,496.811. Add +6.13 ft to convert to the new datum, you get 14,502.94 in the new NAVD88 datum.

At this point in time, the latest NGS Datasheet seems to be GT1811, which lists Whitney at 14,505 ft . Unless there is a newer DATASHEET I'm not aware of, that seems to be the "official" elevation.

I hope this sheds some additional light on the subject. Go Figure.