A paleosecular variation (PSV) curve for western North America is presented on the basis of 94 virtual geomagnetic poles (VGPs) from dated volcanic rocks sampled at 446 sites. Approximately 60% of the paleomagnetic database has been previously published. A curve defined by “spherical smoothed splines” is fitted to the VGPs, ranked by the quality of the age determinations, where the data density is highest between 3690 and −30 years before present (B.P.) (A.D. 1950), between 7800 and 7050 years B.P., and between 14,060 and 12,700 years B.P. The younger segments of the curve derived from volcanic rocks are similar but less complex than other high‐resolution PSV curves derived from lacustrine sediments, particularly the record at Fish Lake, Oregon. The PSV record from lava flows (PSVL), however, is perhaps more reliable in its general shape and chronology because of the higher fidelity of volcanic rocks as magnetic field recorders and because of the greater density of 14C dates. The new PSVL record provides a partial Holocene master curve for western North America and will be of particular value in dating geological and archeological materials using paleomagnetic directions.

The Heise and Picabo volcanic fields of eastern Idaho are part of the more extensive time-transgressive Yellowstone-Snake River Plain hotspot track. Calderas associated with these two silicic volcanic fields are buried under 1 to 3 km of younger basalt, so their locations and eruption record histories have been based on analysis of silicic units along the margins of the eastern Snake River Plain along with some limited geophysical data. A 1.5 km borehole penetrating through basalt into underlying silicic rocks provides new data we used to reassess caldera locations and the timing of eruptions of these volcanic fields. Using these new caldera locations, we calculate an extension-adjusted rate of 2.35 cm/yr for the North American plate over the last 6.66 m.y. and a velocity of 2.30 cm/yr over the 10.27 m.y. Recalculation of a previously determined plate velocity-based migration of the deformation field surrounding the eastern Snake River Plain yields an extension-adjusted rate of 2.38 ± 0.21 cm/yr. These migration rates all fall within the previously published range of North American plate velocities of 2.2 ± 0.8 cm/yr, 2.4 cm/yr, and 2.68 ± 0.78 cm/yr based on a global hot spot reference frame. The consistency of these rates suggest that over the last 10 m.y., the Yellowstone hot spot is fixed with respect to the motion of the North American plate and therefore consistent with a classical deep-sourced hotspot model.

A series of uniformly tilted fault‐bounded blocks is a common feature in actively extending regions, such as the Basin and Range province. If the tilted blocks were produced by rigid “domino‐style” rotation, one would predict large voids at either end of a series of these blocks. Using tilt data and a simple flexural calculation, we suggest that much of the apparent rigid behavior could also be produced by internal block deformation. In our model of normal fault growth, isostatic/elastic uplift of the footwall is coupled with hanging wall downdrop within the region between faults, resulting in the appearance of a tilted rigid block. We present tilt data sampled at varying distances from several block‐defining faults within the northeast Basin and Range province. Tilt measurements between a series of 30‐km spaced block‐defining faults are found to be uniform, while tilts between more widely spaced faults exhibit a pattern of tilt that diminishes to zero in less than 30 km. Using a simple flexural calculation for internal block deformation, we show that for this region the patterns of tilt are consistent with a flexural length scale of ∼8–12 km and deflections of 2–4 km. These estimates are compatible with both the lower limit to seismicity and basin depth determined from earthquake and seismic reflection studies.

Birds can navigate accurately over hundreds to thousands of kilometres, and this ability of homing pigeons is the basis for a worldwide sport. Compass senses orient avian flight, but how birds determine their location in order to select the correct homeward bearing (map sense) remains a mystery. Also mysterious are rare disruptions of pigeon races in which most birds are substantially delayed and large numbers are lost. Here, it is shown that in four recent pigeon races in Europe and the northeastern USA the birds encountered infrasonic (low-frequency acoustic) shock waves from the Concorde supersonic transport. An acoustic avian map is proposed that consists of infrasonic cues radiated from steep-sided topographic features; the source of these signals is microseisms continuously generated by interfering oceanic waves. Atmospheric processes affecting these infrasonic map cues can explain perplexing experimental results from pigeon releases.

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