"The historical map collection has over 48,000 maps and images online. The collection focuses on rare 18th and 19th century North American and South American maps and other cartographic materials. Historic maps of the World, Europe, Asia, and Africa are also represented."
Digitized by A&M University, "the Geologic Atlas of the United States is a set of 227 folios published by the U.S. Geological Survey between 1894 and 1945. Each folio includes both topographic and geologic maps for each quad represented in that folio, as well as description of the basic and economic geology of the area."
Comprehensive search system for locating maps of different areas providing information on geology, hazards, earth resources, geophysics, geochemistry,
geochronology, paleontology, and marine geology. Use GEOSCIENCE MAP CATALOG button to search.
The USGS "brought together two existing images of the Nation's lower 48 states into a single digital tapestry. Woven into the fabric of this new map are data from previous U.S. Geological Survey (USGS) maps that depict the topography and geology of the United States. The resulting composite is the most detailed and accurate portrait of the U.S. land surface and the ages of its underlying rock formations yet displayed in the same image.
"This is the current series of topographic maps, constructed from layers of geographic data – orthoimagery, roads, geographic names, contours and hydrographic features - which can be turned on or all as you create the digital map best for your purposes." Free downloads.
"This guide explains how to access and use USGS topographic maps on the Web: US Topo maps and the scanned collection of paper USGS historical topographic maps, which were printed from the late 1800’s until 2009."