SURFICIAL DEPOSITS: MINING FOR SCIENCE, MINING FOR DOLLARS

Surficial deposits found in the San Juan Mountains are represented by fluvial gravels, debris fans, colluvial deposits, peat bogs, rock glaciers, and glacial moraines. These deposits are a gold mine of information for science and they are a gold mine of wealth for counties and the State of Colorado. Recent mapping and sampling by the US Geological Survey team associated with the Abandoned Mine-lands Initiative has led to a better understanding of pre-mining metal loading. Gillam (1998) has reconstructed the Quaternary history of the Animas River drainage from her work on terrace deposits. Pruess and Jarrett (USGS) reconstructed the catastrophic October, 1911 Gladstone flood event. Pre-historical fire events have been identified by Gonzales, Kenny and FLC students from recently incised alluvial fan deposits. Sand and gravel deposits generate $312 M per year in revenue for Colorado. These gravels are classified as in-stream, floodplain and terrace gravels. The Animas, San Juan, Rio Grande and Dolores rivers have all three types of deposits. The flood plains of these rivers have evolved over the past 12,000 years. The higher terraces are known to be tens of thousands to 600,000 years old. The sand and gravel deposits from the San Juan Mountains consist of granite, gneiss, quartzite, andesite, limestone and sandstone. In the Animas River, granite and quartzite comprise the harder gravel.There are currently over 130 active gravel pit operations in the nine western counties of southwestern Colorado. Eighteen of these are in-stream. La Plata and Montezuma Counties account for 50 percent of these operations. Important questions surround surficial deposits both from the mysteries they hold and from the impact of mining. We still don’t know much about late Quaternary events that may be recorded in high Alpine bogs. What is the heavy metal loading impact from gravel mining and for how long? What are the gravel replacement rates in areas where in-stream gravel mining is occurring? What is the impact of multiple gravel pits on flood hazards, the riparian habitats and migratory paths of elk and deer. We know little about rock glaciers and how/why they move.