Lunar Prospector gamma-ray spectrometer data for surface thorium indicate that craters greater than about 60 km in diameter tend to excavate into materials less Th-rich than the surface regolith. For the largest 12 craters and basins amenable to this type of analysis (diameters between 90 and 930 km), the ratio of crater (or basin) Th concentration to regional background Th averages 0.76¿0.13. This trend implies a pronounced diminution in average Th concentration with increasing depth (down to roughly 30 km deep) in the lunar crust. Assuming deep-origin Orientale ejecta was strongly diluted by turbulent basin-modification mixing, an even more pronounced depth-Th anticorrelation would be indicated by extrapolation of the trend of the 30--300 km craters to higher diameters, i.e., deeper excavations. In any case, the overall lunar crust, and by extension the bulk Moon, is probably far less Th-rich than a simple averaging of surface compositions would suggest. ¿ 2001 American Geophysical Union