Upper Mississippi Valley District

F1 < HEYL, A. V., AGNEW, A. F., LYONS, E. J., AND BEHRE, C. H., JR., 1959, THE GEOLOGY OF THE UPPER MISSISSIPPI VALLEY ZINC-LEAD DISTRICT: U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 309, 310 P.F2 < HEYL, A. V., AND WEST, W. S., 1982, OUTLYING MINERAL OCCURRENCES RELATED TO THE UPPER MISSISSIPPI VALLEY MINERAL DISTRICT, WISCONSIN, IOWA, ILLINOIS, AND MINNESOTA: ECONOMIC GEOLOGY, V. 77, P. 1803-1817.F3 < BROWN, C. E., AND WHITLOW, J. W., 1960, GEOLOGY OF THE DUBUQUE SOUTH QUADRANGLE, IOWA-ILLINOIS: U.S. GEOLOGICAL SURVEY BULLETIN 1123-A, 93 P.F4 < WHITLOW, J. W., AND BROWN, C. E., 1963, GEOLOGY OF THE DUBUQUE NORTH QUADRANGLE, IOWA-WISCONSIN-ILLINOIS: U.S. GEOLOGICAL SURVEY BULETIN 1123-C, P. 139-168.F5 < FLINT, A. E., AND BROWN, C. E., 1955, GEOLOGY AND ZINC-LEAD DEPOSITS IN THE DURANGO AREA, DUBUQUE COUNTY, IOWA: U.S. GEOLOGICAL SURVEY MINERAL INVESTIGATIONS FIELD STUDIES MAP MF 33, 1:12,000.