During April 1999, the U.S. Geological Survey (USGS) conducted a 13-day cruise in the Garden Banks and Green Canyon regions of the Gulf of Mexico (Figures 1 and 2). The R/V Gyre, owned by Texas A&M University, was chartered for the cruise. The general objectives were (1) to acquire very high resolution seismic-reflection data and side-scan sonar images of the upper and middle continental slope (200-1200-m water depths), (2) to study the acoustic character and features of the sea floor for evidence of sea-floor hazards, and (3) to look for evidence of subsurface gas hydrates and their effects.