The United States Geological Survey produces several national series of topographic maps which vary in scale and extent. The USGS Map Locator and Downloader is a convenient tool for seeing what maps are available for the area in which you’re interested. Downloading high-resolution maps is free and many are available for order in hard copy.
The largest (both in terms of scale and quantity) and best-known topographic series is the 7.5-minute, 1:24,000 scale, quadrangle. Each of these maps covers an area bounded by two lines of latitude and two lines of longitude spaced 7.5 minutes apart.
The area covered by each map varies with the latitude of its represented location due to convergence of the meridians. At lower latitudes, near 30° north, a 7.5-minute quadrangle contains an area of about 64 square miles (166 km2). At 49° north latitude, 49 square miles (127 km2) are contained within a quadrangle of that size.