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Wind speeds at the 300 m tower at the Boulder Atmospheric Observatory have been analyzed. This tower is located in slightly rolling farmland. The following conclusions have been reached:(1) For west winds, the terrain is sufficiently uniform for simple surface-layer theory to be adequate without modification even though the air has moved up a small slope to reach the tower. For south and southeast winds, 'effective' roughness lengths must be introduced, which are significantly larger than the 'true' roughness length.(2) Useful wind estimates up to 150 m can be made from winds at 10 m and stability information, provided the 'effective' roughness length is known.(3) The observations are consistent with a von Karman constant of 0.35.