ABSTRACT Arizona has a wide variety of geological features relevant to planetary geology. The “Holey Tour” is a 2 d field trip (Phoenix-Flagstaff-Phoenix) that introduces participants to crater forms (hence the “holes” of the tour), including a maar, karst sinkhole, pit crater, cinder-cone craters, a volcano-tectonic depression, and the classic impact structure Meteor Crater. The Apollo astronaut field training site near Flagstaff is examined, which includes a terrain that was artificially generated to simulate a cratered lunar surface. In addition, planetary volcanism is discussed with stops that include a shield volcano, composite cone, silicic dome, and cinder cones; considerations include key variables in volcanic morphology, such as lava composition and rates of effusion. The general geology of Arizona is discussed throughout the trip and includes parts of the Colorado Plateau, the Basin and Range Province, and the Central Highlands (also called the “transition” zone). The trip can be adapted to meet the needs of any group, from secondary school students to established planetary scientists. This field trip generally follows the GSA guide published in GSA Special Paper 483 (available at https://pubs.geoscienceworld.org/gsa ): Greeley, R., 2011, The “Holey Tour” planetary geology field trip, Arizona, in Garry, W.B., and Bleacher, J.E., eds., Analogs for Planetary Exploration: Geological Society of America Special Paper 483, p. 377–391, https://doi.org/10.1130/2011.2483(23) .

Arizona has a wide variety of geological features relevant to planetary geology. The “Holey Tour” is a 2 d field trip (Phoenix-Flagstaff-Phoenix) that introduces participants to crater forms (hence the “holes” of the tour), including a maar, karst sinkhole, pit crater, cinder-cone craters, a volcano-tectonic depression, and the classic impact structure Meteor Crater. The Apollo astronaut field training site near Flagstaff is examined, which includes a terrain that was artificially generated to simulate a cratered lunar surface. In addition, planetary volcanism is discussed with stops that include a shield volcano, composite cone, silicic dome, and cinder cones; considerations include key variables in volcanic morphology, such as lava composition and rates of effusion. The general geology of Arizona is discussed throughout the trip and includes parts of the Colorado Plateau, the Basin and Range Province, and the Central Highlands (also called the “transition” zone). The trip can be adapted to meet the needs of any group, from secondary school students to established planetary scientists.

Warford Ranch is a small “drive-in” shield volcano covering an area of ~2 by 3 km west of Phoenix, and it is accessible from Interstate Highway 8 near Gila Bend, Arizona. The basaltic shield is superposed on silicic lavas, granodiorites, and alluvial deposits and is part of the Sentinel-Arlington volcanic field. Dated at 3.19 Ma, the shield volcano is sufficiently young to preserve the original morphology, but it also shows the effects of moderate weathering, development of desert varnish, and the formation of caliche deposits. Imaged in both color near-infrared (IR) and in thermal infrared multispectral scanner (TIMS) data, these various units afford the opportunity to conduct simple remote-sensing mapping, which can then be field tested. In addition to the lava flows comprising the shield, pyroclastic deposits and dikes are also present. The compact size of the volcano enables the entire feature to be examined in the field in one day. With short introductory discussion, participants of nearly any background can be introduced to the fundamentals of remote sensing, igneous rocks, field methods, and evaluation of the volcanic history of a small volcano.

The Pinacate volcanic field is ~330 km SSW of Phoenix, and it is a popular destination for volcanology and planetary geology field trips. The volcanic field, located on the Pinacate Biosphere Reserve in Sonora, Mexico, is a 1500 km 2 basaltic field including a shield volcano, lava tubes, maars, a tuff cone, cinder cones, pāhoehoe and ‘a‘ā lava flows as young as 12 ka, and phreatomagmatic constructs as young as 32 ka. We developed an image-based set of exercises for a 2 day field trip focusing on (1) Crater Elegante, a maar crater, (2) pāhoehoe and ‘a‘ā flows near Tecolote Cone campground, (3) the complex eruptive history of Mayo (cinder) Cone, and (4) Cerro Colorado tuff cone. This paper discusses exercises to teach concepts in visible and radar image interpretation and planetary volcanology, and provides an overview of the field trip.

Abstract This chapter treats two areas of the northwestern United States characterized by great late Cenozoic outpourings of basaltic lava. The western part of this region is underlain by flood basalt of the Columbia River Basalt Group. As discussed below by Waitt and Swanson, this area constitutes the Columbia Plain. The laterally extensive, thick cooling units of the Columbia River Basalt Group contrast with the thinner, less extensive flows of the Snake River Plain, which lies to the southeast. Lavas of the Snake River Plain were emplaced coincident with Pliocene-Quaternary rifting, from about 5 Ma to present. Much of the Columbia Plain is overlain by tens of meters of Pleistocene loess, which is extensively dissected to form the rolling topography of the Palouse Hills. In the northeast, broad channels were carved into the Palouse loess and underlying basalt by cataclysmic Pleistocene floods. The characteristic flood erosion of the basalt impressed early settlers as a scaring of the earth by removing its protective soil, and the term “scabland” was applied to it. The best known geomorphic studies in the Columbia Plateau centered on the role of cataclysmic flooding in the origin of its landscape. The central figure in this research for over half a century was J Harlen Bretz (Fig. 1), a glacial geologist at the University of Chicago. Bretz (1923a) used the name “Channeled Scabland” to describe the area of loess-mantled northeastern Columbia Plain that was scoured by flood channels. In 20 major articles and monographs, mostly published between

Earth-based observations and spacecraft results show that aeolian processes are currently active on Mars. Analyses of various landforms, including dunes, yardangs, and mantling sediments of probable aeolian origin, suggest that aeolian processes have been important in the geological past. Dust storms originate in specific areas of Mars and are most vigorous during the martian summer in the southern hemisphere. In order to understand aeolian processes in the low surface pressure (∼7 mb), carbon dioxide atmosphere of Mars, a special wind-tunnel was fabricated to carry out investigations of the physics of windblown particles under martian conditions. Martian threshold wind speeds have been derived for a range of particle diameters and densities; the threshold curve parallels that for Earth but is offset toward higher wind velocities by about an order of magnitude. The “optimum” size particle (the size most easily moved by minimum wind) is about 100 pm in diameter; minimum freestream winds to generate particle motion are about 40 ms-I. Grains smaller than 100 pm (“dust”) require increasingly higher winds to initiate threshold; yet, estimates of grain sizes in the dust clouds are in the size range of a few microns and smaller. Because the Viking Lander has recorded winds no stronger than those for minimum threshold, it is suggested that some other mechanism than uniform strong winds is required for “dust” threshold. Experiments and theoretical considerations suggest that such mechanisms could be cyclonic (“dust devil”) winds, a saltation cascading effect by larger (more easily moved) particles, and injection of fine grains into the wind stream by outgassing volatiles absorbed on the grains.