RideWithGPS

[dodgeman]

If we’re sharing benchmark pictures this is the oldest I found, on the bluff of the Mississippi River near Dallas City Illinois. I also had used the website you posted to find benchmarks.

 

[mschwett]

FWIW, I use RideWithGPS regularly and the altitudes are pretty damn good.
I actually have an old U.S. Coast & Geodetic Survey Base Marker on my property, so I know the altitude there and what I get is within 10ft of that. Maybe it depends on the phone? I'm using an iPhone 14 Pro Max.

i regularly do rides with known "peak" elevations, as well as often being next to the ocean, or in areas of the city where i've done professional work and have elevations burned into my brain. recent iPhone elevations are really very good generally, which make's @Jeremy McCreary's report a little surprising. two weekends ago i summitted mount diablo, which has posted signs every 1,000 feet, at the top of the road, plus a benchmark at a monument. despite a longish ride, changing weather conditions (storms blowing out) the indicated altitude was never more than 20 feet off, and usually closer. very impressive considering the limitations of GPS based elevation in a small consumer device.

i also routinely park my bike at work in a basement garage under a high rise, and even there it's pretty damn close, reading -15 typically. i don't think anyone at apple or google is really telling what all the data used for the elevation readings are, but they're likely some combination of barometry, gps, wifi triangulation, basemaps, who knows what else.

entertainingly, the benchmark at the top of mt diablo may be off by three feet...

Mount Diablo Meridian | The Center for Land Use Interpretation

Most Initial Points are created incidentally, as baselines (and sometimes the meridians) are usually created first, with one end anchored on relatively immutable geographic features, such as the confluence of rivers, or latitudinal lines. The west has a number of exceptions, where prominent...

clui.org

 

[dodgeman]

Interesting read on Mount Diablo. I remember several years ago some idiot journalist decided the mark for the four corners was way off. There happened to be a triangulation station not too far away, but I think it was a couple of miles away. A triangulation station is set in a random location that has good visibility and then its latitude and longitude are determined as accurately as possible, all done originally in the 1930’s. This journalist published a story saying the four corners was off over 2 miles.

 

[tomjasz]

High enough?

 

[Jeremy McCreary]

i regularly do rides with known "peak" elevations, as well as often being next to the ocean, or in areas of the city where i've done professional work and have elevations burned into my brain. recent iPhone elevations are really very good generally, which make's @Jeremy McCreary's report a little surprising. two weekends ago i summitted mount diablo, which has posted signs every 1,000 feet, at the top of the road, plus a benchmark at a monument. despite a longish ride, changing weather conditions (storms blowing out) the indicated altitude was never more than 20 feet off, and usually closer. very impressive considering the limitations of GPS based elevation in a small consumer device.

Beginning to think that my bike resides in its own little space-time bubble.

Used to ride Mt. Diablo in my MTB days in Orinda and know those signs and that summit monument well. The core of the mountain and the sedimentary rocks tilted up toward it on all sides have a remarkable geologic origin. A bike is a great way to explore the rock outcrops that tell the story. If the summit visitors center shop is still open, they'll have something on the subject.

 

[6zfshdb]

If we’re sharing benchmark pictures this is the oldest I found, on the bluff of the Mississippi River near Dallas City Illinois. I also had used the website you posted to find benchmarks.
View attachment 151295

Great find!

The oldest benchmark recovery I submitted to the USCGS was JW0034 or X11 :

It's a chiseled square and not a survey disk. It was monumented in 1871 on the west wall of the Fifteen Mile Creek Aqueduct along the C&O Canal near Little Orleans, MD. It was last located in 1941 and it took over an hour for my brother and I to find. We had to use a whisk broom to sweep off the top of the stone coping.

This is the data sheet with the recovery information I submitted to the USCGS in 2010:

I know it seems like wasted effort but there is a lot of history associated with these benchmarks. A great deal of work went into their placement and there is some satisfaction associated with their recovery. An old surveyor friend once told me their creation in the early 20th century was the modern equivalent of putting a man on the moon.

 

[dodgeman]

1879, that’s a good one. It looks like that must be your recovery note at the bottom. I wonder about the quality of the data on it, the elevation might not check that good.

 

[6zfshdb]

1879, that’s a good one. It looks like that must be your recovery note at the bottom. I wonder about the quality of the data on it, the elevation might not check that good.

Yes, those are my recovery notes from 2010. There is a more recent recovery in 2023 shown on the current datasheet.

The elevation shown on that old Garmin GPS III+ was almost 50' off the 1941 NGS adjusted value. Consequently, I didn't bother reporting it. The handheld coordinates however were definitely more accurate than the NGS estimate. Tree cover makes the station unsuitable for highly accurate "blue book" GPS measurements.

 

[smorgasbord]

Here's the Base Marker on my property:

I haven't yet risked the $250 fine for "disturbing,