SummitPost.org

I was surprised to discover, while browsing the USGS website, that the official elevations of several prominent Sierra peaks seems to fall short of what I thought their elevation was. According to the official elevations posted by the USGS, Thunderbolt Peak, Mount Muir, Middle Palisade, Mount Tyndall and Mount Langley are all lower than 14,000 feet. That means that, officially, there are only 9 fourteeners in California. Polemonium and Starlight are not listed (and never were) because they lack prominence, but Crooks Peak (Day Needle) is listed among the 9.

http://geonames.usgs.gov/pls/gnispublic ... ID:1654923
http://geonames.usgs.gov/pls/gnispublic ... ID:1654925
http://geonames.usgs.gov/pls/gnispublic ... ID:1654979
http://geonames.usgs.gov/pls/gnispublic ... FID:268266
http://geonames.usgs.gov/pls/gnispublic ... ID:1654926

I don't think it's that important, but I wonder if there was a recent systematic revision of Sierra elevations, not yet included in commonly available maps. Does anyone know about this?

Interestingly, North Palisade's elevation increased by 23 feet.

http://geonames.usgs.gov/pls/gnispublic/f?p=gnispq:3:::NO::P3_FID:264233

I'm curious about some of the other major Sierra peaks...

From the FAQ whose link is prominently shown in red at the top of those pages you cited:

"Where do the elevation figures come from?

Elevation figures are not official and do not represent precisely measured or surveyed values. The data are extracted from digital elevation models of the National Elevation Dataset for the given coordinates and may differ from elevations cited in other sources, including those published on USGS topographic maps. Variances between the NED and GNIS elevation data and other sources generally arise from acceptable tolerances, and will be most evident for features such as summits, where precision is of more concern, and where the local relief (rate of change of elevation) may be more prominent. When the elevation figure is of particular note, for example the highest point in the State, then the actual elevation is recorded in the description field of the feature. The elevation figures are sufficiently accurate for most purposes of general information. Efforts are continuously being made to improve the accuracy and resolution of both GNIS and NED data, the results of which will be reflected at both sites."

The most accurate way to get elevations is my using Google Earth and putting the mouse pointer on the highest point of the mountain.

How is sea level detemined ? Is there a point on the Pacific Coast that is used for Sierra peaks ?

Be extremely suspicious of GNIS elevations. The older Rand McNally atlases used them, for example, and often added 30+ feet to a peak's elevation.

Re: sea level... since that can change hourly with the tides, there is no "surveyor's origin" for sea level that I know of. Elevations, lats and longs are all derived from various models of the earth, using geoids. If done well, these geoid models can be very accurate for large sections of the world. However, the world itself is not perfectly spherical, nor symmetric: it's fatter at the equator (prolate) and bulges moreso in the western hemisphere, which explains why peaks in Ecuador are farther from the center of the earth than those in the Himalayas. Yet were we to have one model for the whole world, based on a single mean sea level, we would have cases where actual sea level is above the mean sea level or below it. I don't think that would fly. Riots would ensue. The wikipedia explanation is well-done and uses some $20 words.

Next time you power up your GPS, scroll through the 60 or so datums stored in it, most you'll never use, and most which are highly localized for single regions.

Thunderbolt never was a peak anyway.

It's all Colorado conservative hate propaganda!

surgent wrote:Be extremely suspicious of GNIS elevations. The older Rand McNally atlases used them, for example, and often added 30+ feet to a peak's elevation.

Re: sea level... since that can change hourly with the tides, there is no "surveyor's origin" for sea level that I know of. Elevations, lats and longs are all derived from various models of the earth, using geoids. If done well, these geoid models can be very accurate for large sections of the world. However, the world itself is not perfectly spherical, nor symmetric: it's fatter at the equator (prolate) and bulges moreso in the western hemisphere, which explains why peaks in Ecuador are farther from the center of the earth than those in the Himalayas. Yet were we to have one model for the whole world, based on a single mean sea level, we would have cases where actual sea level is above the mean sea level or below it. I don't think that would fly. Riots would ensue. The wikipedia explanation is well-done and uses some $20 words.

Next time you power up your GPS, scroll through the 60 or so datums stored in it, most you'll never use, and most which are highly localized for single regions.

I'm not sure if you are blurring the ellipsoid and the geoid. Garmin GPS units have had a geoid approximation, which seems pretty good in units sold after 2005. This approximation is added to the ellipsoid calculation.

Get the PID files for mountains like Langley. I bet they have actually increased in elevation relative to the values on the latest maps, as we are now using an earth-centered geoid, and Whitney has increased by about 6-7' in that area.

Values calculated by digitizing older maps are rough, at best. The original maps were done by photogrammetry, and simply don't "see" features like spires. Unless someone did an actual optical survey on checkpoints, or used DGPS, the elevations from photogrammetry are suspect.

Note that Polemonium was misplaced on the USGS maps.

mrchad9 wrote:Thunderbolt never was a peak anyway.

Mr. Chad, having viewed your climber's log I am in awe of your accomplishments. But with all due respect I am curious as to why you include Thunderbolt in your list of peaks climbed and then state that it's not a peak?

By the way, I enjoy the discussion of prominence and the debate over which peaks should or shouldn't be recognized. It's all very fascinating. I aspire to climb as many as I can whether they be official, recognized, published or otherwise.

Simply due to the prominence RickF.

Thunderbolt is a point on the ridge. Of course, that says nothing about whether it is worth climbing or not, but IMHO it is not a summit. There are perhaps a dozen or more pages on SP I have signed that are not true summits, but most were worthwhile objectives.

I've gotten into in depth discussions of this on several occasions, with climbers much more dedicated than me. I think you have to draw the line somewhere, but folks needn't let a point fall from being a worthy objective simply because it isn't a summit. That said, I did sign the log, but when folks asks how many peaks I climbed a season, or how many 14ers, etc... I do not include such destinations.

If Thunderbolt, Polemonium, and Starlight were 14ers then I really hope that person would call Williamson's horns, the needles south of Whitney, and Shasta's west summit 14ers. I hope to make it up Starlight this year... but it won't add a 14er for me!

The reduced number is good - it means we Californians can sell all our gear after finishing only 9 fourteeners instead of 15.

google earth mouse says 14014 ft for mt tyndall and 14497 for mt whitney- seems realistic to me. mt blanc has lost 60ft or so by the mouse test, but the grand teton is up 5ft or more. butler co ohio high pt is printed as 1051ft
but the mouse says 1049ft

johnr wrote:From the FAQ whose link is prominently shown in red at the top of those pages you cited

As someone who's worked with the National Elevation Dataset recently, I want to explain this a bit more. For most parts of the country, the NED comes in 1/3 arc-second resolution, approx. 30 ft. Basically you get a big raster file for each 1 deg x 1 deg block with (60min*60sec*3=10800) rows and 10800 columns. To get the elevation of a given point, you figure out its x and y offset and look it up in the file. There are various interpolation schemes for getting a more exact number when the point lies partway between two entries, but that only gets you so far.

There's also the issue that the source data itself may not have been sampled at 1/3 arc second. Generally they don't get this stuff by tracing out existing topo maps, but by using radar and lidar rangefinding from planes and satellites. If they resampled the original data to fit their standard format, the NED entries may already have a bit of guesswork going into them.

So when they use the NED to look up a peak's elevation, the best they're going to get is a random point within 15 feet of the summit. Depending on where the original data came from, the elevation of that point may already be a guess based on other neighboring points.

Generally the NED and paper topos line up dead on. Occasionally they disagree, and in that case I generally trust the NED for flatter terrain, and regular USGS topos for summits. My understanding of the way the original maps were built is that a lot of effort was put into precisely identifying the location and elevation of prominent peaks, because those were then used as reference points for the surrounding terrain.

Also, I assume Google Earth uses the NED, although possibly with better interpolation than the USGS's website. I know their terrain layer does, because it has the exact same hiccups I found when building a shaded relief layer.