Which to believe?

Back in early February, I headed to Yuma for the Southwestern Arizona Geocachers annual mega event. Lots of fun was had all weekend long and our geocaching adventures took us all over the southwest corner of Arizona. At one point, we came across this benchmark on a canal overdressing. If you look closely, it's an elevation benchmark listing the elevation above sea level as 132.8 feet. I'm not sure when this benchmark was placed, but it was probably placed sometime in the middle of the last century.

When I saw it, I decided to get out my phone and pull up an app that I have on the phone called My Altitude. I've used it in the past and it's proven to be pretty accurate when comparing it to other spots of known elevation. One summer when camping in the eastern Sierras, my friends and I hiked up to the top of Kearsarge Pass out of Onion Valley. This pass tops out at 11,760 feet above sea level according to the sign indicating you're entering Kings Canyon National Park. When I pulled out the phone on that particular occasion the My Altitude app was within about 10 feet of the same numbers. Several other times I've noted that the app was very close to what was an already known altitude.

Which brings me back to this benchmark. I spotted this one and once again decided to see what the app said about the altitude on this bridge. As you can see, there's almost a 30 foot difference in elevation between the posted altitude and what was showing on the app. I have theory behind this which, I think, offers a possible explanation as to why the app was so different from the posted altitude.

Altitudes are constantly being changed and/or as better technology rolls on to the scene. When I was growing up, I remember Mt. Whitney, the highest peak in the contiguous United States measuring out at 14,495 feet above sea level. Yet today, if you look on new maps, you'll see that Mt. Whitney stands 14,505 feet above sea level. What? An earthquake happened and the mountain grew by ten feet? If that had happened, we'd know about it because that kind of earthquake would be common knowledge, especially in this day and age.

What's happened is, over the course of time, new technology has allowed us to measure things more accurately, hence the change in the elevation of Mt. Whitney and other peaks all over the world. Even Mt. Everest in the Himalayas is a different height than when it was when I was a kid. New technology has caused our measurements to be more accurate.

So if this benchmark was embedded into the bridge before the advent of satellites, which is entirely possible, we're looking at probably outdated information on the benchmark. Please notice on the My Altitude app that the elevation is accurate to plus or minus 11.09 feet. So the benchmark could be as high as 172 feet above sea level or possibly only 150 feet above sea level according to the app. Now if we extrapolate it out and say that technology might have added an additional ten feet in actual elevation to where the benchmark was located on the bridge, then we actually fall into the margin of error, especially if the app was measuring things a little bit too "tall" that particular day. 142 feet as opposed to 132 feet on the benchmark and the app could be as low as 150 feet, which means there's only a difference of 8 feet between the benchmark and the app, which is about what I've been seeing ever since I started using the app.

Granted, this is all hypothetical, but that's my best guess as to why the two were so far apart originally. I guess what I need to do is bring out the My Altitude app more often when I come across things that have a posted elevation so I can get more data.

So what are your thoughts on this? Do you think I'm close? Or do you have a different hypothesis of your own that you'd like to share? I'd love to hear your thoughts on this.