Discussion from McGrain and Currens (1978)
Union County is in the westernmost part of the Western Kentucky Coal Field. The Ohio River marks the western boundary, and the Tradewater River forms the southern boundary. The topography varies from broad, flat floodplains with elevations of less than 400 feet along the Ohio and Tradewater Rivers and their tributaries to island-like hill masses that rise 150 to 200 feet or more above the valley flats. Local relief throughout the county is generally less than 100 feet, but some of the hills and ridges overlooking the Ohio are 200 to 250 feet above the river. Steep slopes are not abundant, but bluffs may be found along the Ohio and Tradewater Rivers and in some of the hill areas. Elevations in excess of 600 feet are rare in Union County. The highest elevation in the county is 673 feet, a knob in Chalybeate Hills 2 1/2 miles south of Morganfield. Nearby Spring Hills has an elevation of 640 feet; Bald Hill, 2 miles southwest of Spring Grove, is 620 feet.
The lowest elevation, 320 feet, is at the confluence of the Ohio and Tradewater Rivers at the southwestern comer of the county. Current scars, sloughs, and swamps characterize the floodplain of the Ohio throughout its length in the county. Elevations on the floodplain generally range between 340 and 350 feet.
The elevation of Morganfield, the county seat, is 437 feet. Elevations at other communities are Bordley, 417 feet; Breckinridge Job Corps Center at Whitaker Way entrance, 400 feet; Caseyville, 355 feet; Dekoven, 380 feet; Grangertown, 370 feet; Grove Center, 390 feet; Henshaw, 375 feet; Hitesville, 407 feet; Spring Grove, 416 feet; Sturgis, 375 feet; Sullivan, 377 feet; Uniontown, 365 feet; and Waverly, 407 feet. The elevation of Moffitt Lake is 420 feet.
The 7.5-minute topographic quadrangle maps that cover the county are shown, by name and by index code (Kentucky Natural Resources and Environmental Protection Cabinet) on the index map.