Some 200 previously unreported heat flow measurements were made along a flow line crossing the Juan de Fuca Ridge crest near 47 ¿N. All but one of the multipenetration stations were on the east flank of the ridge, in the thickly sedimented Cascadia Basin. The accuracy of individual penetrations remains low due to the poor penetrability of the basin turbidites, but the multiplicity of the measurements provides a statistical estimate of precision at most stations. The raw heat flow means of the multipenetration stations do not decrease regularly with increasing distance from the spreading center; the lowest measurements are near 70 km from the ridge crest, well onto the turbidite sediment fill of the basin. A basement outcrop near these measurement sites appears to cause the low heat flow by ventilating hydrothermal circulation beneath the sediments. In the eastern part of the basin the sedimentation correction to the observed heat flow becomes significant, and, if the filling of the basin occurred mostly in the Pleistocene, the correction brings those measurements close to the theoretical heat flow of cooling lithosphere. Extrapolated basement temperatures reach nearly 200 ¿C beneath the eastern basin, a region where the magnetic anomalies become noticeably weaker than those closer to the ridge. They do not, however, disappear entirely, as might be expected from some laboratory measurements of blocking temperature. ¿ American Geophysical Union 1987