Certain tuffs, sampled near active faults in northern California, exhibited the same large electrical resistance changes with stress reported by Yamazaki for tuffs from the Izu Peninsula. These effects, studied in the laboratory, were most pronounced at stresses below 6 MPa, for partial saturation, and for rocks with porosity less than 20%. Relative changes of resistance with strain reached 105 for several of the tuffs near a strain of 10-4. A curious and unexplained aspect of the electrical behavior of the tuffs was the recoverability between stress cycles; this was not observed for other, equally porous rocks like sandstone and for partially saturated granite. Electrically sensitive tuffs near active faults might be used in earthquake prediction studies provided field sites in partially saturated tuffs can be found.