The map depicts a 100-mile radius centered on the area just south of Denver at a scale of 5 miles to the inch. The map illustrates the hydrology of the region, along with a simple pattern showing the Continental Divide and downplaying the complex topography of the region. It illustrates a proposed project to create 2 power plants on the South Platte River, a dam on the Tarryall River, and a canal feeding land owned by the Company just north of Castlerock, Colorado. Colorado’s rich agricultural and mineralogical production is highlighted by colored medallions, along with $57,000,000 in manufactured goods in the Denver area in 1903. Most of the medallions reflect production in 1903, while those for gold and silver appear to be aggregate figures. Near Greeley, a medallion for sugar beet production features a faint pencil note indicating that by 1924 it had grown to $45,000,000 per annum in 1924.
The following advert appeared in the journal The Electrical World for March 16, 1907:
Fred Nexon, of this city is offering electric energy at two and one-half cents per kw-hour. The offer is made on behalf of the Tarryall Power & Reservoir Company, which is being promoted by Chicago capitalists, who contemplate the construction of a plant on the Platte River to be completed by the end of the year. (vol. XLIX, no. 11, p. 570).
The damming of the Platte was contemplated as far back as 1890, when a company calling itself the Tarryall Irrigation Company was incorporated. This map seems to relate to an attempt to promote the project in the early 1900s, though the dam and reservoir were not constructed until 1929 and 1931.
I find little information about Laurence Tenney Gray, who seems to have been heavily involve in the economic development of Colorado in the early 20th century, though whether as an engineer, investor, manager or combination thereof is not clear. Some of his papers are held at Colorado College, and the brief catalog note suggests he was involved in “the Ophelia Tunnel (a.k.a. the Moffat Tunnel), The Tarryall Dam Project, La Veta Coal, and Cripple Creek mines and railroads.”