The theme of the 2004 GSA Annual Meeting and Exposition, “Geoscience in a Changing World,” covers both new and traditional areas of the earth sciences. The Front Range of the Rocky Mountains and the High Plains preserve an outstanding record of geological processes from Precambrian through Quaternary times, and thus serve as excellent educational exhibits for the meeting. With energy and mineral resources, geological hazards, water issues, geoarchaeological sites, and famous dinosaur fossil sites, the Front Range and adjacent High Plains region provide ample opportunities for field trips focusing on our changing world. The chapters in this field guide all contain technical content as well as a field trip log describing field trip routes and stops. Of the 25 field trips offered at the Meeting, 14 are described in this guidebook, covering a wide variety of geoscience disciplines, with chapters on tectonics (Precambrian and Laramide), stratigraphy and paleoenvironments (e.g., early Paleozoic environments, Jurassic eolian environments, the K-T boundary, the famous Oligocene Florissant fossil beds), economic deposits (coal and molybdenum), geological hazards, and geoarchaeology.