Colorado Historical Society: http://www.coloradohistory.org/

Colorado Preservation, Inc. (CPI): http://www.coloradopreservation.org/

The Documentation and Conservation of Buildings, Sites and Neighborhood of the Modern Movement (docomomo): http://www.docomomo.com/

National Register of Historic Places, National Park Service: http://www.nps.gov/nr/

National Trust for Historic Preservation: http://www.preservationnation.org/

National Park Service's Recent Past Initiative: http://www.nps.gov/history/hps/tps/recentpast/index.htm

Recent Past Preservation Network: http://www.recentpast.org/