By Beth Simmons

Recent Earth Movements. An Account of Some Movements in the Rocky Mountains as Shown by Effects on Streams and Mines, by Professor Arthur Lakes, Mines and Minerals, Dec. 1902, V. 23, #5, p. 228 (excerpts)

Most people are aware that great movements of the earth’s crust have taken place in past ages. Geologists also know that these movements have progressed up to the present time and, we may add further, are still in progress. The general opinion of geologists nowadays, we believe, is that past movements have been relatively slow and gradual, and rarely paroxysmal, sudden, or sharp, though some movements have undoubtedly been more rapid than others. It is interesting, therefore, to observe what movements in the earth’s crust have gone on comparatively recently, and what we have reason to believe are today in progress, and what we can actually see in progress in our own lifetime.

Before approaching the subject of movements in the present time, we may mention briefly one or two orographic movements that we have reason to believe are comparatively recent or at least postquaternary.

In the Arkansas cañon, near Leadville, a series of lake deposits forms prominent table lands for some miles between the towns of Granite and Leadville. These lake beds were deposited after the glacial epoch. The sediments composing them have locally been consolidated by iron oxide into a conglomerate rock, and these strata have been tilted from 10 to 25 degrees by the subsequent rising of the mountains around them either by the Mosquito or Sawatch Range since the last Glacial epoch.

Along the foothills of our mountains on the eastern slope, near Boulder, especially, the lake terraces show a decided dip to the east away from the mountains; these lake beds are certainly postglacial.

Of more recent local movements we have ample evidence in landslides. The base of Aspen Mountain is formed by a series of landslides, which have evidently slipped off from the concave shell of granite that forms the backbone of that thin “knife-edge” mountain. The direct cause of this slipping is doubtless an underlying bed of tilted slipping shale, overlain by a water- sponge of porous diorite porphyry. That these landslide movements of the past are still continued is shown by the fact that shafts put down in Vallejo Gulch to reach the so-called “contact” could not be kept in line, but were perpetually closing in and moving down hill. It may be of some significance that Aspen Mountain is the theater of the greatest and most intricate faulting movements of any mining region known to us in the State.

“Earthquakes have doubtless had indirectly much influence in bringing about landslides, by the jar of the shock and liberation or direction into new channels of subterranean waters.

“On January 1, 1894, an earthquake occurred with the usual vibratory and other accompaniments. In the volcanic ‘stocks’ the earthquake was not perceived, but in the bedded volcanics it was generally observed on the surface near Telluride which is located on gravel and at Red Mountain, six miles east in the direction from which the wave is said to have come. Red Mountain, be it observed, is nearer the supposed former focus of volcanic activity and has been the scene of much solfataric action.

“In the succeeding summer and thereafter, the flow of streams, both surface and subterranean, was much smaller than before and the miens were in consequence much inconvenienced. This diminution, while due in part to the disturbance, is also in part due to the deep draining of the talus mounds. It is likely that slight earthquakes are more common than generally believed in this region.

“An important part played in the production of landslides is by the percolation of surface waters through the porous volcanic complex and San Miguel conglomerate to the sandy Mancos shale, and by the partial plasticity of the last named thus brought about with each returning spring.”