Geology is among the most visual of the sciences, and spatial reasoning takes place at various scales and in various contexts. Among the spatial skills required in introductory college geology courses are spatial rotation (rotating objects in one's mind) and spatial visualization (transforming an object in one's mind). Geologic curricula commonly require students to visualize Earth in many ways, such as envisioning landscapes from topographic maps, the interaction of layers and topography, and the progressive development of geologic features over time. To facilitate learning in introductory college geology laboratories, we created two geologic modules— Visualizing Topography and Interactive 3D Geologic Blocks. The modules were developed as learning cycles, where students explore first, are then introduced to terminology and concepts they have observed, and finally apply their knowledge to different, but related problems. Both modules were built around interactive QuickTime Virtual Reality movies that contain landforms and geologic objects that students can manipulate on the computer screen. The topography module pairs topographic maps with their three-dimensional (3D) representations on the same screen, which encourages students to visualize two-dimensional maps as three-dimensional landscapes and to match corresponding features on the map and 3D perspective. The geologic blocks module permits activities that are not possible with normal paper-based curricula, such as interactively rotating, slicing into, eroding, and faulting the blocks. Students can also make the blocks partially transparent to reveal the internal geometry of layers, folds, faults, intrusions, and unconformities. Both modules encourage active participation by having students describe, draw, and predict, and both modules conclude with applications that require the students to extend and apply key concepts to novel situations. Assessment of the modules using control and experimental groups shows that the modules improved student performance on a geospatial test, that general spatial ability can be improved via instruction, and that differences in performance between the genders can be eliminated by a semester-long laboratory. “To go out into the field with a geologist is to witness a type of alchemy, as stones are made to speak. Geologists imaginatively reclaim worlds from the stone they're trapped within.” – Frodeman (1996 , p. 417).

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Abstract The Granite Wash Mountains are located in west-central Arizona and are contiguous with the Harcuvar Mountains to the northeast and the Little Harquahala Mountains to the south. They are part of the Maria fold and thrust belt, a belt of large folds and major thrust faults that trends east-west through west-central Arizona and southeastern California (Reynolds and others, 1986; Spencer and Reynolds, 1990). In the Granite Wash Mountains, late Mesozoic deformation related to the Maria belt affected a diverse suite of rock units, including Proterozoic crystalline rocks, Paleozoic carbonate and quartzose clastic rocks, and Mesozoic sedimentary, volcanic, plutonic, and hypabyssal rocks. This deformation was mostly deep seated and produced an assortment of folds, cleavages, and both ductile and brittle shear zones. Several discrete episodes of deformation occurred, resulting in refolded folds, folded and refolded thrust faults, and complex repetition, attenuation, and truncation of stratigraphic sequences. Greenschist-facies metamorphism accompanied deformation and was most intense along the major thrusts. Deformation and metamorphism were followed by emplacement of two Late Cretaceous intrusions and numerous Cretaceous to mid-Tertiary dikes.

Reconnaissance mapping indicates that parts of nine mountain ranges previously considered to be Precambrian basement are instead variations of Tertiary metamorphic core complexes. From southeast to northwest, these ranges include the Pinaleno, Picacho, South Mountains, parts of the Buckeye, White Tank, Harquahala, Harcuvar, Buckskin, and Rawhide Mountains. Together with the already recognized Santa Catalina–Rincon–Tortolita complex, these ranges define a broad northwest-trending belt through Arizona. The northeast-trending Buckskin-Harcuvar-Harquahala Mountains are transverse foliation arches, the latest expression of a huge, northwest-elongated metamorphic area herein named the Harcuvar metamorphic core complex. This Tertiary phenomenon is superimposed on an ill-defined center of late Mesozoic metamorphism. Traverses into the complex from its unmetamorphosed southwestern margin reveal progressive Cretaceous conversion of Mesozoic sedimentary rocks into migmatites. Metamorphism just preceded intrusion of the Tank Pass batholith, an Upper Cretaceous pluton which itself became foliated and involved in early Tertiary migmatization and intrusion in the Harcuvar Mountains. A marginal zone of penetrative mylonitization, capped by a more brittlely deformed dislocation surface, flanks the Harcuvar complex on its upper and broadly arcuate northeastern margins. Resting on this tectonic surface are highly tilted, unmetamorphosed, layered rocks (Paleozoic to Tertiary). Geochronologic and geologic data place the time of mylonitization as Tertiary, perhaps as recently as 25 to 20 m.y. B.P. This deformation (flattening and northeast-southeast extension) was closely followed by development of chlorite breccia, the dislocation surface, thick wedges of coarse clastic sediment, and listric faulting. Finally, the core complex was arched and uplifted. A model for this sequence of events is predicated on mobile northeast-directed extension of a flat upper-crustal layer facilitated by intense mid-Tertiary plutonism in an actively tensile stress field. Tectonism in a brittle, surficial upper plate is governed by listric faulting and detachment as the plate fragments and extends “piggyback” style upon subjacent, ductilely stretched layer.

Rocks in the South Mountains of central Arizona are representative of rocks found in metamorphic core complexes elsewhere in Arizona. These core-complex terranes are in part characterized by low-angle mylonitic foliation that contains penetrative northeast-trending mineral lineations and pervasive smearing out of mineral grains. In the South Mountains, mylonitic rocks form a doubly plunging, northeast-trending foliation arch and have been derived from Precambrian amphibolite gneiss and a composite mid-Tertiary pluton. The pluton is undeformed in the core of the arch, but shows a progressive increase in pervasiveness of mylonitic fabric up structural section. Mylonitic plutonic rocks are exposed as a carapace overlying their less-deformed equivalents. Mylonitically foliated Precambrian amphibolite gneiss is restricted to a zone underlain and overlain by nonmylonitic (crystalloblastic) gneisses that are lithologically identical and largely retentive of their Precambrian foliation. Fabrics in mylonitic rocks indicate extension parallel to the east-northeast–trending lineation and flattening perpendicular to the gently dipping foliation. The fabric is well dated as late Oligocene to early Miocene (25 to 20 m.y. B.P.). Mylonitic deformation was followed by more brittle deformation which produced a chloritic breccia that overlies mylonitic plutonic rocks in the northeast half of the arch. The chloritic breccia is probably related to normal faulting along a low-angle dislocation surface.

Recent field work and accumulated Rb-Sr studies, when combined with previous U-Th-Pb and K-Ar investigations, allow a new synthesis of the crystalline terrane within the Santa Catalina–Rincon–Tortolita crystalline complex. When all the available data are integrated, it is apparent that the crystalline core is mainly a composite batholith that has been deformed by variable amounts of cataclasis. The batholith was formed by three episodes of geologically, mineralogically, geochemically, and geochronologically distinct plutons. The first episode (75 to 60 m.y. B.P.) consisted of at least two (and probably three) calc-alkalic, epidote-bearing biotite granodiorite plutons (Leatherwood suite). The Leatherwood suite is intruded by distinctive leucocratic muscovite-bearing peraluminous granitic plutons (Wilderness suite), which are 44 to 50 m.y. old. At least three Wilderness suite plutons are known, and their origin has been much debated. Leatherwood and Wilderness plutons are intruded by a third suite of four biotite quartz monzonite to granite plutons (Catalina suite) that mark the final consolidation of the batholith 29 to 25 m.y. ago. Much of the mylonitic (cataclastic) deformation of the plutonic rocks and recrystallization of the enclosing host rocks may be related to intrusion of the various plutons. At least three episodes of mylonitization (cataclasis) may be delineated by observing relations between mylonitic and nonmylonitic crosscutting plutons. The southern part of the Leatherwood pluton bears a moderate to strong mylonitic foliation that is cut by undeformed leucogranites and pegmatite phases of the Wilderness pluton. Elsewhere in the Santa Catalina–Rincon–Tortolita crystalline core, Wilderness suite plutons contain penetrative mylonitic foliation. Foliated Wilderness suite plutons are intruded by an undeformed portion of a Catalina suite pluton. In the Tortolita Mountains, however, intrusions of the Catalina suite themselves contain evidence for at least two events of mylonitic deformation. The most significant of these events is clearly constrained to the Catalina intrusive episode because it formed during or after the emplacement of Tortolita quartz monzonite (about 27 m.y. B.P.) but before the intrusion of postfoliation dikes (about 24 m.y. B.P.). All three episodes of mylonitization contain the distinctive and much discussed east-northeast–trending lineations. All events of mylonitization are constrained to a 50-m.y. interval of time from 70 to 20 m.y. ago. Although continuous mylonitization from 70 to 20 m.y. ago cannot be unequivocally disproved, the strong association of mylonitization with the three plutonic episodes suggests that deformation in the Santa Catalina-Rincon-Tortolita crystalline core, like intrusion, was episodic.