Tintic, Sioux-Ajax Tunnel

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This page was last updated on September 17, 2025.

Overview

(The focus of this page is the surface workings of the Sioux-Ajax tunnel, as visible in photographs, as well as a general description with minimal coverage of the geology and financial returns. Also to establish a timeline using sources not previously readily available.)

The Sioux-Ajax Tunnel connected the area near the Ajax mine on the Mammoth (west) side of Sioux Peak, with the area near the Sioux mine on the east side of Sioux Peak.

The Sioux-Ajax tunnel is located at the head of Mammoth Basin, north of the Ajax mine. It was being driven eastward into Mammoth Mountain, and as of 1898, was somewhat over 3,000 feet in length.

Tintic Mining and Development Company was organized as a subsidiary of the Tintic Company, in August 1896 in West Virginia, and reorganized in January 1906 in Maine. A joint mortgage was made in 1910 that included Yampa Smelting Company and West Mountain Tramway Company as security. (The Copper Handbook, Volume XI, 1912-1913, page 879)

Sioux-Ajax Tunnel

April 4, 1896
A new enterprise known as the Sioux-Ajax Tunnel was started with the goal of driving a tunnel 4,000 feet, extending the existing Ajax tunnel's current 600 feet, under Sioux Peak, to the Sioux property on the east side. The mouth of the Ajax tunnel was at the head of Mammoth Hollow, about 1000 feet south of the Mammoth mine. The new tunnel would allow the ore from many mines to be transported to the surface, and be further transported by the recently announced New East Tintic railway to either the Mammoth or Sioux mills, or to its interchange with Union Pacific and Rio Grande railroads. (Salt Lake Tribune, April 4, 1896)

(There were reports as early as June 1895, before the Sioux mill was built, that the Sioux company would approach the Mammoth company to connect the two properties underground, which would reduce transportation costs for the Sioux company by giving it access to the planned Mammoth railroad. The Mammoth company's tunnel was 1,200 feet "under cover" and would require extending 3,000 feet to reach Sioux ground. -- Salt Lake Herald, June 12, 1895)

January 4, 1897
The Sioux-Ajax Tunnel had reached 1,550 feet. (Salt Lake Tribune, January 4, 1897)

December 26, 1897
The following comes from the December 26, 1897 issue of the Salt Lake Herald.

The Sioux-Ajax Tunnel. -- Eighteen months ago, Manager Geo. H. Robinson, of the Tintic Mining & Development company, began work on a tunnel, with the intention of tapping the ore bodies of the Sioux and Utah mines, and intervening properties, from the Mammoth side. The distance is about one mile, and 3,000 feet of a double-track tunnel eight feet high, had been driven when work was discontinued, late last summer. On Dec. 1 work was resumed, and ten men and two Burleighs are working by day and by night, to complete the work. When finished, it will enable the company to unload their ore by means of an underground tramway, into cars of the new East Tintic railway, on the opposite of the mountain range. From there it is a short haul to the Oregon Short Line and Rio Grande Western at Mammoth, so that the ore is handled but once from the mine to the smelter. In the meantime the Sioux is practically idle, but is in good shape to resume ore shipments at any time.

At the Utah Mr. George Robertson is working a force of 18 men on a lease, and is extracting considerable good ore. The Sioux-Ajax tunnel, besides the Ajax, will pierce several other good properties, which will be worked through it, and will be the means of a great deal of development in and around Mammoth mountain. It is by far the most expensive and important work in the district.

February 8, 1900
President Henry Stern of the Tintic Mining & Development Tunnel company was in town, on his way to Denver then to New York. He and George H. Robinson and others were interested in the tunnel enterprise at Tintic. "What would be done with the tunnel in which work was suspended over six months ago, he said he really did not know. The matter of whether it would he continued was entirely in the hands of Mr. Robinson - but the gentleman intimated that if electric power could be obtained to operate drills, the work might be resumed. The tunnel has its starting point between the Mammoth end Ajax properties, and is headed for the Sioux-Utah possessions on the opposite side of the mountain. It is now in a distance of a mile or so, but it is not known that any great strikes have so far been made." (Salt Lake Herald, February 8, 1900)

April 8, 1900
"The Tintic Mining & Development company has sold its seven-drill compressor plant and the pipe line which runs from Robinson to the tunnel, to the United States Mining: company. It will be made to do service on the latter company's Bingham mines in the future. It is reported that the former company will put in an electric plant at the mouth of its long tunnel when operations are again commenced." (Salt Lake Herald, April 8, 1900)

April 6, 1901
At the time the Tintic Mining & Development company bought the Yampa mine in Bingham Canyon, the Sioux-Ajax tunnel at Tintic was 4,000 feet long. (Deseret News, April 6, 1901)

January 10, 1901
"A Sioux-Ajax Rumor. -- George H. Robinson the eminent mining engineer and chief expert for F. Auguat Heinze in the latter's scrap for supremacy 1n Montana, came down from Butte yesterday and is again applying himself to interests at this end of the line. While nothing definite is known concerning Mr. Robinson's intentions, it has been rumored for some time around Tintic he would resume work on the Sioux-Ajax tunnel, which has been driven for nearly 4,000 feet into the backbone of Tintic and at the same time take up the exploration of territory owned by his company upon the tunnel's margins." (Salt Lake Tribune, January 10, 1901)

July 31, 1901
"After allowing its vast tract of mineral land in Tintic to be practically idle for nearly 2 years, the Tintic Mining & Development company has started prospecting again. Frank Evans, who came in from Mammoth this morning, stated that the machinery was all in place and the fires were to be lighted today. The latest work consisted in setting in place the new Imperial Rand drill compressor. It has a capacity of 7 drills and it is the intention of the management to run the plant up to its full capacity as noon as the compressor is limbered up. For the present the company expects to start a force of about 12 men prospecting in the tunnel which has been run into the hills of Tintic fully 3,000 feet." (Deseret News, July 31, 1901)

February 2, 1912
"The systematic prospecting of the property of the Tintic Mining & Development Co., this work to be handled through the old Sioux-Ajax tunnel. This tunnel is one of the longest in the entire district and reaches clear from the Mammoth-Gold Chain side of the Mountain to the Carisa mine. The ground of the Tintic Mining & Development company came in for a great deal of development work some years ago but recently it has been in the inactive list. The development of such splendid ore bodies in the Gold Chain and Opohongo mines as well as strikes in the old Mammoth mine no doubt caused a revival of interest in the ground of the Tintic Mining & Development Co. The claims which this company owns are to the north east of the Gold Chain and, as any map of Tintic will show, the ground is exceptionally well located." (Eureka Reporter, February 2, 1912)

September 28, 1913
"The work which has been going on for the past year or two in the property of the Tintic Mining & Development company at Mammoth has been stopped temporarily. This company’s ground takes in the old "Sioux-Ajax" tunnel and adjoins the Gold Chain. Opohongo and Mammoth properties. At the time a shaft was sunk from the main tunnel level it was understood that the management was trying to locate the Gold Chain ore, which should extend over into the neighboring property. Work has been carried on to a depth of 800 feet, and while the showing has been favorable on that level no values have been found." (Salt Lake Herald, September 28, 1913)

Yampa Mine and Smelter

February 28, 1901
The Yampa mine was organized to develop the Yampa group of claims, which had been sold to Tintic Mining and Development Company in February 1901 by Colonel Enos A. Wall, for cash and 5000 shares in the Tintic company. The purchase of the Yampa group in Bingham would allow the Tintic company to expand its operations outside of the Tintic mining district, where it also owned the Sioux-Ajax group, with the intent of operating the Tintic and Bingham properties under one management. The actual sale and transfer of property took place on April 6, 1901. The purchase price was reported as $150,000. (Salt Lake Mining Review, February 28, 1901; Deseret News April 6, 1901, "today")

The Yampa mine was owned by the Tintic Mining and Development Company, which also owned mines in the Tintic mining district. The Tintic company owned 30 claims on 180 acres, located on Carr Fork in Bingham Canyon, but development was confined to the Yampa mine, situated on less than six acres that were completely surrounded by the claims of the Utah Consolidated company. Ore from the Yampa mine was transported by way of the West Mountain Tramway Company, also controlled by the Tintic company. The tramway was 12,270 feet in length, built to the Leschen design, and was the longest in the Bingham district, with a 700 tons daily capacity. The mine had ore bins of 600 tons capacity. Production was sent to the Yampa smelter, but in 1909 a contract was made with the Garfield smelter. (The Copper Handbook, Volume 11, 1912-1913, page 879)

Yampa Smelting Company was organized in 1903, with its stock being controlled by the Tintic Company. The property included the smelter located in lower Bingham Canyon, built in 1904 and enlarged in 1906 to 1000 tons daily capacity. The smelter was connected to the Yampa mine by the aerial tramway of the West Mountain Tramway Company. The Yampa smelter included ore bins, a calcining building, and a blast furnace building, all with steel frames. A converter section, in its own building, was added in 1907, but was shut down in 1909. The smelter was a small plant that could not compete commercially with the much larger custom smelters located in the Salt Lake valley, and at Garfield. The Yampa smelter processed the low-grade copper ore from the Yampa mine, but when that mine made a contract with American Smelting Company at Garfield, the Yampa smelter shut down its plant in August 1910. (The Copper Handbook, Volume 11, 1912-1913, page 981) The smelter equipment was sold in 1914. (The Mines Handbook, Volume 13, 1918, page 149)

February 9, 1907
The parent company of the Yampa mine and smelter, Tintic Mining & Development Company was controlled by Capt. Henry Stern of New York City, and his associates. Yampa Smelting Company was a subsidiary, along with the Britannia mine in British Columbia, the Britannia smelting company, with works in Crofton, Vancouver Island, and a large copper mine in Alaska. The Yampa smelter at Bingham was capable of receiving 400 to 500 tons per day, but was not operating at full capacity due to poor transportation facilities, and lack of fuel. (Deseret News, February 9, 1907)

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