Clastic dikes in sedimentary rocks. In northern Colorado, the contact between the upper Fountain and lower Ingleside Formations (Lower Permian) is sometimes marked by enigmatic clastic dikes. Present in the uppermost strata of the Fountain, they appear to have formed during or slightly after deposition of the overlying Ingleside. Are they tectonic in origin or perhaps they formed by the infilling of loose sand from dessication cracks at the Ingleside paleosurface? The image is from Lory State Park near Bellvue Colorado, where the initial view is to the north