Concrete Arrow is a Remnant of a US Airmail Beacon Station, Timpie Junction in Skull Valley

US Air Mail arrow, north end of Skull Valley.
Designation SALT LK AWY BN 59.

This large concrete arrow in Utah’s West Desert is part of the old Post Office Airmail system. These arrows are scattered all over the country but this one is my favorite because access is easy in that 1) it is on public land, and 2) it is right off Exit 77 of I-80.

Just a few years after the Wright Brothers' first flight, airplanes were used sporadically to carry the mail. During WWI, significant advancements were made by the US Army (no Air Force until after WWII) in airplanes and they had proven their utility.

So, in 1918 the Post Office asked the Army to create a system to fly mail on a regular basis for faster delivery. The Army developed and ran the airmail for the first 3 months using converted Army planes.

The Army then handed the system off to the Post Office to manage. Initially airmail only ran in the eastern states but slowly the rest of the US was included.

By Sept of 1920, airmail was flown across the country, from NYC to San Francisco, but only by day because night flying was difficult due to the inability to see the railroad tracks that they typically followed. So, a national system of night beacons atop concrete arrows showing the way was developed to guide the pilots.

As usual, Utah’s West Desert was a challenge and took until 1929 to complete the east-west transcontinental route. Each arrow pointed the direction to the next arrow on the route, typically 10-15 miles away.

Atop the tower was a rotating beacon with 2 directional spotlights showing the proper direction. Red lights were chosen over white lights as they could be seen from a farther distance. Green lights were used when there was an emergency landing strip nearby.

Mail Arrow beacon layout.
Excerpt from Air Navigation by P. V. H. Weems 1938

This was the system the airmail used for decades. Innovations in the technology that aided pilots were constantly developing. And eventually, the air beacons became unnecessary.

The Timpie airmail beacon was dismantled in May 1965 along with several others in Salt Lake and Tooele Counties.

This arrow was painted orange by a local boy scout troop, about 2017. Historically the arrow would have been yellow.  

Arrow in May 2022

Here is how the arrow looked in 2016, before it was painted. 

And here are various maps of the airmail routes: 

United States Post Office Department map of air mail routes, 08/21/1928.
(Source)

Clip of the 1924 airmail route, showing Salt Lake City to Timpie, via Grantsville.
From US Army, Air Corps, US Army Corps of Engineers & Geological Survey, USTB. (1924) Aeronautical strip maps of the United States.

Source: Library of Congress, https://www.loc.gov/item/2009582531/.

There is lots of information available about these US Airmail beacons and their concrete arrows. The two sites I like are below:

• Google Map of Concrete Arrows
• Arrows Across America

Update Sept 1, 2022:

I added video directions to the arrow from Exit 77 of I-80 in Tooele County, Utah.

Kennecott advertisement from 1969

Check out this Kennecott advertisement from the 1969 Polk Directory.

Note that this is before I-80 was constructed on the west side of SLC.

And before the construction of that massive Kennecott tailings pond that is now just off of Utah Route 201 (2100 South).

At the time (and for quite a while) the Bingham Canyon Mine was the largest man-made open pit mine on the planet.

Ancient Footprints Persevered in the Great Salt Lake Desert

Ancient footprints are preserved in the Great Salt Lake Desert.  An excavated footprint is in the foreground but you can also see unexcavated footprints (which appear like darker shadows in this image) in the background. July 2022.

Hill AFB recently announced a unique archaeological site in the GSL Desert on their South Bombing Range.

Named the Trackways Site, it consists of several tracks of human footprints likely dating to about 12,000 years ago.

Thousands of Paleo-age archaeological sites have been found in this area of the GSL Desert, including the famed Wishbone Site with a radiocarbon date on a fire hearth of 12,300 years ago. Although the finding of intact human footprints is surprising, it is in line with previous discoveries in the area.

The archaeologists are being cautiously optimistic about the authenticity of the find, citing more research is required.

I visited this site a short time before the official press release; I went in skeptical and left fairly convinced of its human antiquity. The stratigraphy is what ultimately convinced me.

Nowadays, that area of the GSL Desert is a wide-open alkali flat almost void of all flora and fauna, which means most people avoided it for most of the last 10,000 years.

The GSL Desert was once the bottom of Lake Bonneville in which fine silts were deposited on the lake floor. Then, during the waning years of Lake Bonneville, the area became a vast wetland fed by overflow water through the Old River Bed and springs, thus creating a vast wetland known as the Old River Bed (ORB) Delta.

The type of sediment deposited during each of these stages also changed from the fine silts of a deep lake to the sands and gravels transported by faster flowing streams.

These unexcavated footprints are inverted sand-filled prints. The sand erodes at a slower rate than the surrounding Lake Bonneville silt, These footprints are a part of a longer footprint trackway. July 2022.

The footprints themselves appear to have been formed when people walked in the shallow water of this ancient wetland. Their feet sunk through the sand into the underlayer of fine Bonneville silts, which were then filled in with the overlayer of sand after the foot was removed. Consequently, the footprints were preserved as sand-filled imprints, some of which are now exposed as inverted sand prints surrounded by alkali flats.

Here is the link to the original Hill AFB press release. 

Lake Bonneville Animation

I made a thing! Of course, it is of my favorite Pleistocene-age closed-basin lake system = Lake Bonneville!

Also, I had to make a YouTube channel, so I guess you can check that out too.

Salt Lake County in Relation to Lake Bonneville

The Salt Lake Valley has Lake Bonneville shorelines on the west (Oquirrh) and east (Wasatch) sides of the valley. You just need to look at the mountainsides to see those etched horizontal lines (the Provo and the Bonneville being the easiest to spot).

But it is also fun to see where those shorelines are in areas where it is more difficult to spot them, like under the built environment of our cities.

This map shows how the cities of Salt Lake County are situated in relation to the shorelines.

More about Lake Bonneville!

Lake Bonneville was a Pleistocene-age lake (the last Ice Age). Similar to how the Great Salt Lake is today, the shorelines of ancient Lake Bonneville responded to changes in climate; the lake level increased when it was wetter/cooler and it lowered when it was warmer/drier.

Lake Bonneville was one of several closed-basin lake systems in the Great Basin during the last Ice Age; Lake Lahontan in Nevada being the largest but lots of little ones too. If you find yourself on a playa anywhere in the Great Basin, then you are at the bottom of an ancient lakebed.

The maps in my post show the geographic extent of Lake Bonneville overlayed on top of a modern map. I will detail the SLC area in my next post. The images are in order of highest elevation to lowest, but not in chronological order.

The Stansbury level is the oldest of the main shorelines. The final image shows the Great Salt Lake modern low (today).

Lake Bonneville was a cold freshwater lake. The highest mountain tops (Wasatch, Deep Creeks, etc) had large glaciers and the lake had its fair share of icebergs floating around, it was the Ice Age after all.

My interest in Lake Bonneville relates to the first people living in our area. It’s unclear exactly when people first inhabited the Bonneville Basin. Clearly, people did not live underwater but the shorelines certainly were utilized at some point.

Archaeological evidence shows that people were living and working along shorelines, at least around the Gilbert phase during the Pleistocene-Holocene transition.

A human-made fire hearth documented at the Wishbone archaeological site in the Great Salt Lake Desert shows people were in this area at least by 12,300 years ago. It seems that at least parts of the lake at this time supported freshwater fish and there is direct evidence of Mammoths and waterfowl present, making it an attractive place for ancient people.

Paul Inkenbrandt has put together a fantastic Story Map of Lake Bonneville that you should check out. https://storymaps.arcgis.com/stories/f5011189bdc94545b9231d56e4ffc1e4

Identifying the Bonneville Shorelines

Those large terraces seen on the mountains throughout Utah are the shoreline remnants of Lake Bonneville which covered most of northern and western Utah during the Pleistocene (the last Ice Age). More about the geographic history of Lake Bonneville later.

A wide overview of the north side of the Oquirrh Mountains at the Kennecott Smelter. The 3 main shorelines are highlighted.

A more detailed view of the same location.

The first thing is to start spotting and identifying the primary 3 shorelines seen along the Wasatch Front and throughout Utah’s West Desert.

Those three shorelines are named (from highest to lowest):

Bonneville:
The Bonneville shoreline is usually the easiest to spot, it is the highest in elevation and thus marks the lake at its peak. The Natural History Museum of Utah sits along this shoreline as does the Salt Lake Flight Park (paragliders) in Draper. The Bonneville Shoreline Trail generally follows this shoreline.

Provo:
Provo is also a prominent shoreline, visible in most places where the Bonneville Shoreline can be seen. It often has draperies of tufa (a calcium carbonate precipitate, best known for the tufa “spires” in Mono Lake). The Provo shoreline was formed when the lake overflowed at Red Rock Pass in Idaho. The continued erosion of this natural dam caused the lake to recede quickly and drain to the ocean through the Snake River. The lake stabilized at the Provo shoreline level.

Stansbury:
This shoreline is more subtle than the Bonneville or Provo. The Stansbury shoreline is the oldest of the 3 main shorelines and has been eroded and reworked by the later Bonneville and Provo shorelines. As such, it is only visible in certain areas.

There is also the Gilbert Shoreline, but that is a whole different post. There are lots of active investigations and discussions about the Gilbert. And it is generally hard to spot so I have excluded it here.

I like this image from Utah's Department of Natural Resources G.K. Gilbert Geologic View Park that shows the lake levels of each shoreline in relation to landmarks of Salt Lake City.  

Image from Utah DNR, link to storymap.

Now you get to try to spot the shorelines:  

Same view of the north side of the Oquirrh Mountains at the Kennecott Smelter, without labels.
Photo was taken May 2022.