The underground workings of the United Empire Colliery are about 0.6 kilometre north-northeast of the confluence of Allison (One Mile) and Deer Valley creeks, 4.5 kilometres northeast of Princeton.

This coal deposit is situated at the eastern faulted margin of the Princeton Basin, a northerly trending half-graben superimposed on volcanics and sediments of the Upper Triassic Nicola Group. The basin is separated into a northern and southern area by the gentle, northwest-striking Rainbow Lake anticline. The northern area, in which the deposit occurs, consists of a gently folded, homoclinal panel which is tilted east. Dips commonly range from 15 to 25 degrees east and flatten to the east. The basin is bounded and cut in places by a number of approximately north to northeast-striking, westerly dipping faults. The main faults are the Asp Creek fault and the Boundary fault.

The United Empire Colliery is hosted in a sequence of sandstone, shale, waterlain rhyolite tephra (tuff) and coal, up to 2000 metres thick, comprising the Eocene Allenby Formation (Princeton Group). Locally, the coal-bearing strata strikes roughly north and dips 45 to 60 degrees west. Production originated from two seams separated by 14.0 metres of sandstone, with minor clay, shale and coal. The upper seam is 2.7 metres thick and contains a 15-centimetre thick band of clay. The lower seam is 1.1 to 1.2 metres thick, including a 10-centimetre thick rock band, and is underlain by 2.1 metres of mixed coal and clay. The lower seam has been traced from surface and underground workings over a strike length of 450 metres and a vertical elevation of 76 metres.

A bed of dark brownish grey clay, 15 to 61 centimetres thick, overlies either the upper or lower coal seams. The clay is smooth and plastic, and contains scattered particles of carbonaceous matter. A sample of clay absorbed 29 per cent water and shrank by 9.3 per cent while drying in air (Geological Survey of Canada Memoir 65, page 22). The average tensile strength when air dried was 96 pounds per square inch. The clay burns buff at lower cones, but changes to brown at higher ones. Other firing characteristics are as follows (Geological Survey of Canada Memoir 65, page 22):

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Cone Fire shrinkage Absorption

(per cent) (per cent)

010 1.7 16.76

05 4.1 13.25

1 6.3 9.04

3 7.4 7.85

5 7.4 3.2

9 - 0.9

15 Nearly fused

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The material is not considered a fireclay, but it burns to a good colour, suitable for pressed brick and can be dry pressed.

The colliery was initially developed by United Empire Mining Company between 1908 and 1911. Production commenced in 1912 and continued to 1914. The mine was reactivated by Red Triangle Coal Company in 1932 in order to extract coal left in pillars. The coal was found to be of inferior quality and production was therefore halted in 1933. Total production between 1912 and 1933 amounted to 2531 tonnes. Most of this coal was used in the nearby cement plant of British Columbia Portland Cement Company (092HSE169) in 1913 and 1914.