Probably the most remarkable basalt unit of the stratigraphic record is the late Cenozoic (Pliocene or Pleistocene) Mesa basalt of the northwestern United States. Various lines of evidence show that several occurrences of medium to light gray porous-textured olivine basalt in Oregon, northeastern California, northwestern Nevada and southwestern Idaho apparently are the preserved remnants of a single, regionally extensive lava flow. The thickness of the flow averages only 30 feet and the areal extent must have exceeded 100,000 square miles. It is therefore the world’s largest known lava flow representing a single volcanic event of catastrophic magnitude. Several problems for uniformitarian geology presented by the Mesa basalt are discussed. Widely divergent dates on various portions of the basalt seem to invalidate the potassium-argon dating method. Because the Mesa basalt and many other late and middle Cenozoic basalts were deposited in a subaerial environment, while pre-cenozoic lava flows were usually submarine, it is suspected that the Mesa basalt and other late and middle Cenozoic basalts flowed after the Noachian Flood. This inference is supported by the observation that pre-cenozoic flood strata (widespread dolostone, bedded chert, black shale, coal and graywacke) are uncommon in the late and middle Cenozoic.