USGS - Science for a Changing WorldUnited States Geological Survey is a "federal source for science about the Earth, its natural and living resources, natural hazards, and the environment." The site provides access to a number of different resources. Among those are the Publications Warehouse - "Availability of content ranges from USGS Store purchase, to full text, to bibliographic citation only," Geological Information - "Includes links to major USGS geoscience databases and programs as well as resources for creating digital geologic maps," National Water Data - "provides a comprehensive gateway to water-resources data collected at approximately 1.5 million sites in all 50 States, the District of Columbia, and Puerto Rico." The site also has an educational section designed mainly for K-12 students and teachers. It provides access to information about USGS employment opportunities, student employment, post-doctoral employment programs, intern programs, and volunteer opportunities.