The large, lava-like boulders on the southwest corner of Lafayette’s Waneka Lake, about 100 yards south of the boat house and picnic structures, are remnants of the sizable slack coal dump from the Electric/Summit coal mine that operated from 1898 to 1918. The former Northern Colorado and Interurban Power Plant that operated from 1906 to 1924 also dumped coal ash at the site.
The Electric/Summit coal mine dumped overburden, also called gob, from the mine onto the slag pile and onto bricks left from the power plant’s construction. A powdery remnant of coal, called slack, often spontaneously combusted, causing the heated overburden (usually shale) to fuse into baked shale and take on the reddish-black color. The reddish color is caused by oxidation. This metamorphic process is described in the USGS bulletin Baked Shale and Slag Formed by the Burning of Coal Beds.
There are several large baked shale rocks along the Coal Creek trail at Old Laramie Trail street and adjacent to the former coal dump site of the Vulcan mine. Many Lafayette households have used the baked shale rocks from slag heaps as decorative elements in landscaping. The reddish fused shale was also used as road base for Lafayette’s streets and sidewalks and as fill material for construction projects.
Coal from the Electric/Summit was used to fire the power plant’s steam boilers. The expended coal — the coal ash — was cleaned out of the furnaces after it cooled and then hauled on an elevated trestle and dumped with the mine’s slack coal and overburden.
Northern Colorado Power Company constructed the 6,000 kilowatt Northern Colorado and Interurban Power Plant in 1905-06. It supplied alternating current to the electric-powered Interurban passenger trolley service that connected Boulder to Denver. Joseph J. Henry of Denver developed the business plan and directors included W.F. Crossley, Tyson Dines, W.H. Allison, Sen. F.E. Warren (from Wyoming), William J. Barker, Thomas Kelly, Robert S. Ellison, William Mayer and C.C. Bromley.
Blue Ribbon Hill east of Lafayette was initially thought to be the best place for the new electric plant, due to the presence of Coal Creek water. The power plant was instead located at what is now Waneka Lake. Boulder County Clerk records show that Mary Miller bought the reservoir in 1904 from William, Frank and Guy Harmon, but the Harmons retained rights to some of the water flowing into Miller and Harmon Reservoir.
Northern Power documents from 1906 and reservoir records at the Colo. Div. of Water Resources both show that the original name of Waneka Lake was “Henry Waneka No. 1 Reservoir.” State records indicate that the lake was built by Adolf Waneka in 1865 to hold water coming out of a nearby spring. Adolf gave his interest in the lake to his son, Henry “Boye” Waneka, who then sold to William, Frank and Guy Harmon in 1897. Northern Power expanded the lake, which was later called Plant Lake, in 1906 to store 28 million cu. ft. of water for its steam generators. Mary Miller and the power company split 50/50 the rights to the additional water stored.
Alternating current electric lights started to be switched on in Lafayette homes in about 1907. Alternating current lights were also installed in coal mine tunnels and electric-powered trams began to operate in local mine haulageways. Mules were still used to haul coal from the coal face to the haulage way.
According to Public Service Company, now Xcel Energy, the Interurban Power Plant grid was among the first successful central generation and power distribution systems in the country. The grid supplied power to Lafayette, Louisville, Longmont, Loveland, Fort Collins, Boulder and most of Northern Colorado, including coal mines and sugar beet factories. Northern Power changed its name to Western Light and Power in 1914 and was acquired by Public Service Company in 1923. After the Valmont electric generation plant was built near Boulder in 1924, Lafayette’s Interurban Power Plant was used on standby basis. It last operated in 1948 and was torn down in the 1950s.
Except for some of the large rocks seen today (that couldn’t be broken apart), the lava-like slag pile was probably leveled out, then a shallow layer of topsoil was brought in for the now gently sloping hillside. It’s most likely the reason there are no trees growing in the field.