The Devils Hole calcite vein contains a long-term climatic record, but requires accurate chronologic control for its interpretation. Mass-spectrometric U-series ages for samples from core DH-11 yielded (230)Th ages with precisions ranging from less than 1,000 years (2sigma) for samples younger than approximately 140 ka (thousands of years ago) to less than 50,000 years for the oldest samples ( approximately 566 ka). The (234)U/(238)U ages could be determined to a precision of approximately 20,000 years for all ages. Calcite accumulated continuously from 566 ka until approximately 60 ka at an average rate of 0.7 millimeter per 10(3) years. The precise agreement between replicte analyses and the concordance of the (230)Th/(238)U (234)U/(238)U ages for the oldest samples indicate that the DH-11 samples were closed systems and validate the dating technique in general.

Devils Hole, in southern Nevada, is a surface collapse into a deep, planar, steeply dipping fault-controlled fissure in Cambrian limestone and dolostone. The collapse intersects the water table about 15 m below land surface and the fissure extends at least 130 m deeper. Below water, most of the fissure is lined with a >30-cm-thick layer of dense maxillary calcite that precipitated continuously from groundwater for >500,000 yr. The thick mammillary calcite coat implies a long history of calcite-supersaturated groundwaters, which, combined with the absence of dissolutional morphologies, suggests that Devils Hole was not formed by karst processes. Devils Hole is located in a region of active extension; its tectonic origin is shown by evidence of spreading of its planar opening along a fault and by the orientation of its opening and others nearby, perpendicular to the northwest-southeast minimum principal stress direction of the region. Most Quaternary tectonic activity in the area, including seismicity and Quaternary faults and fractures, occurs on or parallel to northeast-striking structures. The hydrogeologic implications of this primarily structural origin are that fracture networks and caves opened by extensional tectonism can act as groundwater flowpaths functionally similar to those developed by karst processes and that, during active extension, transmissivity can be maintained despite infilling by mineral precipitation. Such extensional environments can provide conditions favorable for accumulation of deposits preserving long, continuous paleoenvironmental records. The precipitates in Devils Hole store chronologies of flow system water-level fluctuations, hydrochemistry, a half-million-yr proxy paleoclimate record, evidence of Devils Hole's tectonic origin, and probably atmospheric circulation.

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A chronology of diving activities and underground surveys in Devils Hole and Devils Hole Cave, southern Nevada, is presented for 1950-86. The report acknowledges the efforts of past underwater explorers, scientists, and observers of the cavern system, and provides a historical perspective for comparison with present investigations at that site.

A new sampler, the horizontal intragravel pipe, was developed for collecting samples ofintragravel water in salmonid spawning gravel. The device is a 2.54 x 76.2-cm length of slotted polyvinyl chloride pipe that is buried perpendicular to flow in the streambed. The slots (about 320/pipe) through which the intragravel water flows were cut perpendicular to the long axis of the pipe. Each slot is 1.9 cm long by 0.15 mm wide. A rigid plastic tube (0.64 cm inside diameter) centered axially within the intragravel pipe is perforated with three 3.2-mm holes equally spaced along its length to distribute equally the effect of pumping. The interior tube is connected by Tygon tubing to a peristaltic pump on a platform above the water surface. Intragravel water is pumped to containers for on-site measurement of dissolved oxygen, pH, and specific conductance, and for determination of other constituents in the laboratory. The principal advantages of a horizontal intragravel pipe are that a substantial quantity of water can be withdrawn for analysis, and samples of water may be integrated across an artificial redd.