This Record describes a seismic refraction survey at Callide Creek 49.8-mile dam site, near Biloela, Queensland. The survey was made at the request of the Queensland Irrigation and Water Supply Commission. Depths to unweathered bedrock and other rocks were determined by their seismic velocities and are shown on cross-sections. From general geological information and the results of drilling in the area, the seismic velocities can be translated into geological terms. Comparison with drilling results suggests that seismic depth estimates are about 18 per cent too low. After correcting this systematic error, the depth determinations are accurate to within 10 ft. Young's modulus for the unweathered bedrock, determined by the seismic method, is estimated at about 7 to 9 x 10,000,000 lb/in2.