Online guide to the continental Cretaceous-Tertiary boundary in the Raton basin, Colorado and New Mexico

Sites to See

Trinidad to the Long Canyon K-T site

Note mileage and turn off I-25 to Colorado Highway 12 and proceed west out of Trinidad. Trinidad Sandstone caps the high ridge to the north of town and crops out along the highway after leaving the outskirts. The entrance to the road across Trinidad Lake dam is near the top of the formation and sandstone, mudstone, and carbonaceous shale and coal beds of the Vermejo Formation are well exposed in high roadcuts on the right. At about 5.7 miles is the approximate position of the base of the Raton Formation. Beds and stringers of pebble conglomerate generally occur at the base of the Raton, but they are commonly absent in this area and the base is represented by beds of sugary-textured quartzose sandstone.

At the town of Cokedale is the large Asarco coal mine waste pile on the right and rows of brick coke ovens on the left that produced coke for the Asarco smelters for 40 years until the mine closed in 1946.

About 1.5 miles past Cokedale watch for the sign to the Watchable Wildlife Area and turn left across the new bridge over the Purgatoire River, cross the railroad tracks, and bear left down the gravel road. Upstream along the railroad the K-T boundary sequence crops out in railroad cuts for several hundred meters beneath a tabular splay sandstone bed that is easily visible from the highway across the valley.

Where the road turns south up a small valley (about a ¼ mi), the K-T boundary claystone is exposed directly beneath a prominent sandstone bed in a steep roadcut known as the Madrid East site. The boundary claystone (the thin, 1-in-thick, white claystone bed at the top of the cut) lies beneath a 2-in-thick coal bed that is directly overlain by the sandstone. The claystone bed is underlain by a brownish-orange-weathering, boney coal bed about 12 to 16 in thick. The claystone bed at this site and in this area exhibits all of the characteristics of the boundary claystone in the Raton basin: anomalously high concentrations of Ir, shocked quartz, the fern-spore spike, and the palynological extinction horizon, all indications of asteroid impact.

Proceed on the road about 2 mi to Long Canyon and turn left at the road junction about 1/2 mi to the parking area for the Watchable Wildlife Area.

Next: Stop 1 - Long Canyon K-T Boundary Site

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