The 1876 Explosion at Arsenal Hill

On April 5 1876, a large explosion rocked Salt lake City.

The powder magazines behind the old city wall and containing about 45 tons of explosives (gunpowder, blasting powder, dynamite, Hercules powder, and Giant powder) exploded on Arsenal Hill (now known as Capitol Hill).

Salt Lake City in 1870 showing the locations of the Arsenal and
Powder Magazines in relation to other landmarks.

Salt Lake City in 1862 showing the locations of the Arsenal and
Powder Magazines in relation to other landmarks.

Arsenal Hill was named after the Arsenal Building which was located near the present location of the DUP Pioneer Museum.

It was not the Arsenal building that exploded, it was four magazine buildings located outside of the old city wall on the western edge of City Creek Canyon, approximately where the Capitol Hill Water Tanks are now located (about 100 E Girard Ave (560 N)). Two were built of brick and two were built of rock.

Three sequential blasts hurled large boulders and debris, blowing out windows, damaging buildings, and killing several people.

The Salt Lake Tribune reported in gruesome detail about body parts strewn about near the center of the blast. What could be gathered of the human remains were picked up and taken to City Hall “where many people went to see them.”

Brigham Young’s Empire Mill in City Creek Canyon (aka the “Witches House” in City Creek) was nearly destroyed.

Nearly a thousand windowpanes of the Mormon Tabernacle building were destroyed, complicating the upcoming LDS General Conference meeting.

Some people believed judgement day had come, others thought perhaps an earthquake or a volcanic eruption. And still others thought Fort Douglas had finally decided to attack SLC with cannon fire and drive the Mormons out of the Salt Lake Valley.

The inquest determined that the most likely cause of the explosion was due to target shooting of two teenage boys who were tending to cattle in the area. A burning paper wad shot from a gun ignited loose powder that was strewn around the magazines.

Not everyone was satisfied with this explanation, especially the Salt Lake Tribune. But no other explanation was put forward.


Additional update:

Using modern data processed by ChatGPT (so it could be totally bogus) I attempted to correlate the historic data with modern understandings of blast overpressure. I then overlayed this information on a modern aerial view of Salt Lake City to view in more familiar surroundings.

In order to do this, first the energetics of a gunpowder explosion needed to be converted to a TNT equivalent as that is a more standard measurement in modern times. And from that, the overpressure can be calculated which can then be correlated to modern data about building destruction as assembled by federal agencies such as FEMA, FAA, and the DoD.

In my simplistic mapping and calculations, I did not take into account any terrain features that would change the on-the-ground impacts.

So, with all that in mind.... 

ChatGPT says:

• The explosive power of gunpowder is significantly lower than that of TNT. Gunpowder has an energy density of approximately 3 MJ/kg, while TNT has about 4.184 MJ/kg. This means that gunpowder has about 72% of the explosive power of TNT.
• To estimate the TNT equivalent of 45 tons of gunpowder:
• Convert tons to kilograms: 45 tons = 45,000 kg
• Calculate total energy of gunpowder: 45,000 kg × 3 MJ/kg = 135,000 MJ
• Convert to TNT equivalent:135,000 MJ ÷ 4.184 MJ/kg = ~32,250 kg of TNT and 32,250 kg = 32.25 tons of TNT
• So, the explosion in 1876, if it involved 45 tons of gunpowder, would be roughly equivalent to 32.25 tons of TNT in modern terms.
  
  
• To estimate the overpressure effects of a 32.25-ton TNT explosion and analyze its impact on suburban buildings using FAA and DoD guidelines, we conclude with the following results: A 32.25-ton TNT explosion would devastate a suburban neighborhood within 100-200 meters, cause moderate damage up to 500 meters, and break windows up to a kilometer away.
  
  
• Buildings constructed in the 1870s were vastly different from modern suburban structures in terms of materials, construction techniques, and overall resilience to blast effects. Compared to modern reinforced concrete and steel structures, these buildings were far more vulnerable to blast overpressure.
  
  
• How Blast Effects Translate to 1870s Buildings

Overpressure (psi)	Effect on 1870s Buildings
0.1 - 0.3 psi	Light wooden structures may lose windows and suffer minor wall damage. Masonry buildings may have cracked walls.
0.5 - 1 psi	Most wooden homes collapse or suffer severe roof damage. Masonry buildings experience cracked or partially collapsed walls.
1 - 2 psi	Masonry walls fail, wooden buildings completely destroyed.
2 - 5 psi	Total destruction of all wooden and masonry buildings.
5 - 10 psi	Near-ground-zero obliteration of all structures.

Distance from Blast (m)	Expected Damage (1870s Buildings)
100 m	All wooden and masonry buildings destroyed.
200 m	Wooden buildings flattened, masonry severely damaged or collapsed.
500 m	Wooden buildings badly damaged or destroyed, brick buildings may partially collapse.
1 km	Masonry buildings may suffer cracked walls, wooden buildings lose roofs.
2 km	Minor damage, primarily broken windows.

Final Takeaway (from ChatGPT):  If an explosion of this scale occurred in 1876, it would have wiped out most buildings within at least 200 meters, left few standing at 500 meters, and damaged structures up to a kilometer away. In contrast, modern buildings—especially steel-reinforced ones—would generally survive at greater distances with only repairable damage.

Modern aerial image of Salt Lake City. Rings show the distance from the blast central point at 100, 200, 500, 1000, and 2000 meters.  At the 2000 meter mark (outermost ring), 1870s buildings would have minor damage, primarily broken windows.

Modern aerial image of Salt Lake City. Rings show the distance from the blast central point at 100, 200, 500, and 1000 meters. At the1000 meter mark, 1870s masonry buildings may suffer cracked walls and wooden buildings lose roofs.

Modern aerial image of Salt Lake City. Rings show the distance from the blast central point at 100, 200, and 500 meters. At the 500 meter mark, 1870s wooden buildings would be badly damaged or destroyed, and brick buildings may partially collapse.

 

SLC’s redlining map from the 1930s

A redline map of Salt Lake City from the 1930s. Another interesting and important map.

Federal Home Loan Bank Board. Home Owners' Loan Corporation. 1933-7/1/1939.
From the National Archives.

Clip of the map legend. From the National Archives.

During the Great Depression, the Federal Home Loan Bank Board created residential security maps to indicate the risk of default on federally-backed mortgages.

Demographic information, such as race, was used to create these maps.

Green and blue neighborhoods were considered less risky areas to issue a mortgage and usually had majority-White populations. They were described as “best” and “still desirable” neighborhoods.

Often these neighborhoods had restrictive covenants that prohibited people of color from living in the neighborhood. The Westmoreland neighborhood of SLC is an example of this.

Yellow neighborhoods were designated as “definitely declining” and seen as places where “undesirable populations” may increase.

Red neighborhoods were “hazardous” and were associated with higher populations of people of color. Red neighborhoods were ineligible for federally backed mortgages making it difficult for residents in the neighborhood to become homeowners.

Thus, the term “redlining” refers to those red or “hazardous” neighborhoods that tended to have a higher percentage of residents that were people of color.

These maps recorded the existing conditions of the 1930s and then they were used to reinforce and perpetuate segregated neighborhoods.

This map is from the National Archives, direct link: https://catalog.archives.gov/id/85713738

I geo-referenced the redlining map and overlayed modern neighborhood boundaries using GIS. Even today, much of today's neighborhood boundaries align with the redlining map.

The 1930s SLC Redlining Map, with modern Community Council districts, overlayed. 

Detail clip of SLC's Redlining Map, showing Avenues, Downtown, Central City, East Central, University, and Liberty Wells neighborhoods.

Detail clip of SLC's Redlining Map, showing Rose Park, Fairpark, and Capitol Hill neighborhoods.

Detail clip of SLC's Redlining Map, showing Poplar Grove and Glendale neighborhoods.

Detail clip of SLC's Redlining Map, showing East Central, Wasatch Hollow, and Sugar House neighborhoods.  Note that the old State Prison (Sugar House Park site) is identified as "Yellow."

Detail clip of SLC's Redlining Map, showing Yalecrest, Foothill/Sunyside, and Wasatch Hollow neighborhoods.

Maps by W.D. Rishel

Maps are fun! This 1917 map from the Salt Lake Tribune shows SLC as the Crossroads of the West, although the specific verbiage used in the description was “automobile touring center of the west.” Where the tourist must top for supplies and information… whether traveling east, west, north, or south.

This 1917 map was made by W. D. Rishel, manager of the Utah Automobile Association, and shows several travel routes. You will note that many of these routes eventually evolved into our Interstate Highway system while others (notably the Lincoln Highway through Fish Springs) were abandoned.

• Lincoln Highway

• Midland Trail

• Pike’s Peak Route

• Arrowhead Trail

• Evergreen Highway

• Yellowstone Highway

Source: Salt Lake Tribune 1917-12-30 Page 46

Oldest Standing Houses in Salt Lake County, Per Tax Assessor GIS Records

I found some new-to-me, publicly available GIS data showing the oldest standing buildings in Salt Lake County and made this snazzy map. I'm a bit skeptical of some of this data as I've noticed the tax data from the Salt Lake County Assessor is problematic with older homes.  Looks like a field trip to me!  Verification is definitely needed.

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.

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

An 1899 map of Salt Lake City's neighborhood plats

Salt Lake City map, Published by W.H. Whitney, August 1st 1889

Maps are fun! This map from 1899 is new to me. It is a real estate map of SLC showing the various platted neighborhoods.

Some examples:

Image 2: Glendale Park Addition

Image 3: Fort Douglas and Red Butte Creek. Poperton Place is the prominent Pink cutout north of Fort Douglas.

Image 4: Utah Driving Park Race Track (500 E 2100 South)

Image 5: Hot Springs Lake (neighborhood to the west in red is near Northwest Middle School)

The official description is "Compiled from the Records and Actual Surveys By Simon F. Mackie, Civil Engineer. Published by W.H. Whitney, August 1st 1889"

There are plenty of sites on the internet that would love to sell you this lovely map, but don't fall for that.

You can download your own copy from Stanford University's Barry Lawrence Ruderman Map Collection.

URL: purl.stanford.edu/sy439kf2563

Native Place Atlas- some Native names of Salt Lake County

The Native Place Atlas is a project from the American West Center at the University of Utah.

Overview of the Native Place Atlas

From their website:

Place names in the United States are officially kept by the US Board on Geographic Names, which was first created in 1890 to address conflicting names and spellings that faced mapmakers in the American West.

The place names that appeared on the first maps of the West derived from Euro-American explorers, surveyors, and settlers. Native presence became “under-mapped” as the cartographic tools of settler-colonialism reconstructed the imagined landscape through place naming.

Out of respect for tribal knowledge and to safeguard against non-Native trespass, the map will not name or show the location of sacred sites.

Unlike drawings of territorial tribal boundaries, which are static and limiting due to the changing nature of these lines throughout history, Native Places allows viewers to see the spread of Native homelands through their linguistic presence.

The data currently contains nearly 600 place names.

https://nativeplacesatlas.org/

Map showing Native Placenames for Salt Lake County vv

Excerpt of Salt Lake County Native Placenames

Salt Lake City's Old GreekTown is Being Eaten Away by Demolition and Development

Map showing new and current construction (2021)
along 200 South and between 500-600 West

Four major construction projects have or will demolish all but 5 of the historic buildings along 200 South between 500-600 West. This section of 200 South was, until recently, one of the better-preserved historic streetscapes representing the historic Greek and Italian ethnic neighborhoods of SLC.

SLC’s Old GreekTown once encompassed the area northwest of Pioneer Park: between the two Railroad Depots (Union Pacific at South Temple and 400 West and the Rio Grande at 300 South and 350 West) and along 200 South between 200 West and 600 West.

In the pre-pandemic era of 2019, there were 12 remaining historic buildings along 200 South between 500-600 West; this was down from nearly 30 historic buildings lining the block in 1950.  After all the current construction is completed there will be 5 historic buildings remaining.

The four projects are:

1. Central Station at 549 W 200 South: This 65-unit apartment project has demolished the 3 Thomas Electric Co buildings in 2020.
2. Central Station West at 577 W 200 South: This 65-unit apartment project has recently demolished the building previously known as the Bricks/Club Sound/In the Vue nightclub.
3. The Cinq at 530 W 200 South: This 203-unit apartment project will preserve most of what remains of the historic Central Warehouse building (520 W 200 South) and will demolish the Citizens Investment Co Building (most recently known as Metro Bar/Café Orbit) at 540 W 200 South.
4. Greenprint Gateway at 592 W 200 South: This 150-unit apartment project will demolish the Green Manufacturing Co (most recently an automobile repair shop) built 1940 at 568 W 200 South. 

Of note, the existing Artspace Bridge Projects complex at 511 W 200 South built in 2001 demolished the buildings associated with SLC Greek Boss Nicholas D. Stathakos; you will remember his story from his house at 963 E200 South that I profiled as part of the “China Blue” rezone proposal a few months ago.

What will be left will be part of the Central Warehouse (520 W 200 S), Am Furniture Manufacturing (566 W 200 S), Michael Shoenfeld Studio (560 W 200 S), the Hong Kong Teahouse (565 W 200 S), and the Corum Building (561 W 200 S).

This stretch of Old GreekTown is part of the Warehouse National Historic District (Boundary Increase) which was designated in 2016 to incentivize historic preservation through the availability of federal tax credits.  The designation of a *National* Historic District does not offer any legal protections against demolition, only the designation of a *Local* Historic District at the city level mandates a review through the SLC Historic Landmark Commission. None of the buildings along 200 South between 500-600 West are Local historic landmarks or within a local historic district.

Green Manufacturing Co (most recently an automobile repair shop) built 1940 at 568 W 200 will be demolished as art of the Greenprint Gateway project.

Most of the buildings in this photograph from 2016 have been demolished. The Thomas Electric Co (beige buildings on the left) and the Bricks/Club Sound/In the Vue nightclub (red buildings at right). For now, the the Hong Kong Teahouse (obscured by trees, but right of the grey building), and the Corum Building (grey building, center of photo).