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The mean temperature at Walden, Colorado is 31.1°F and fluctuates between 15°F and 78°F. The average growing season is 102 days and the average number of frost-free days is 46. Winds are predominantly from the west. Geology The general geology of the North Park region has been well-established by many United States Geological Survey investigations, the most notable of which are Beekly (1915), Hail (1965, 1968) and Kinney (1970, 1971). The North Park region can be geomorphically classified as an intermontane basin, enclosed by the Medicine Bow Range to the east, the Park Range to the west, and the Rabbit Ears Range to the south. The resultant structural basin is truncated to the north by the Independence Mountain Fault. This basin contains sediments ranging in age from Triassic to Quaternary. The Bourg Mine is on the northeastern edge of the McCallum anticline and within a faulted synclinal wrinkle, the Bourg syncline. The syncline on the Bourg property dips a maximum of 41° on the southwest, 15° on the northeast, and plunges 7° to 8° on the northwest. The coal-bearing unit at the Bourg Mine is the Coalmont Formation consisting of coal, shales, siltstones and sandstones. The Coalmont Formation overlies the Pierre shale and underlies gravels derived from pediments in the immediate area. Portions of two coal seams within the Coalmont Formation were mined, the Hoyle Seam and the Sudduth Seam. In addition to the broad synclinal fold that formed the general structural basin of the North Park region, considerable local folding and faulting has also occurred. These local folds and faults are probably the result of compression caused by the formation of the larger synclinal trough. The McCallum Anticline lies between the Michigan and Canadian Rivers, east of the town of Walden. Structurally, the anticline is doubly plunging and is asymmetric about its axis. To the north, where the anticline plunges northwest, the strike is approximately N45°W. To the south, the structure begins to change strike as the crest of the anticline plunges almost due south. Except near both noses, the anticline tends to be asymmetrical, with the more steeply dipping limb to the east side. At the nearby Marr and Canadian Strip mines, the sediments on the eastern flank are near vertical or even overturned. In the area of the Bourg Mine, the strata on the east limb of the McCallum Anticline dip as much as 41° to the northeast. The Bourg Mine is flanked on the northeast by the Ballinger Anticline. The axis of the Ballinger Anticline joins the axis of the McCallum Anticline in Section 21, T9N, R78W. The Ballinger Anticline plunges to the northwest and strikes N35°W. The McCallum and Ballinger Bourg Strip Mine. C-81-021 4 April 21, 1993