1. This study is of the evaporation rates at four different heights, representing increasing degrees of exposure, on the walls of a precipitous canyon in the Starved Rock, Illinois, region. 2. Observations covering a period between July 1 and September 20 showed a similar seasonal march in evaporation rates for all four stations, with the high point in mid-July and the low point in September. 3. As between individual stations, the evaporation rate at the highest and most exposed position was between three and four times that at the lowest and least exposed. 4. An appreciable increase in evaporation, due to insolation, was obtained only at the station located above the level of the tree tops.