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Lineament zone is obscure and cannot be traced beyond the area

                                                                                               just southwest of Las Vegas, where the Cordilleran fold-thrust belt

                                                                                               also appears to terminate in the complexly faulted Mojave region

                                                                                               of eastern California (e.g., figure 14 in Burchfiel et al., 1992).

                                                                                               The Lewis & Clark transverse zone (Fig. 1), which King (1969)

                                                                                               used to separate the central from the northern Cordillera, is

                                                                                               similar to the Texas Lineament in that it ends at the Laramide

                                                                                               thrust belt, and most units north and south display sinistral sepa-

                                                                                               ration or are truncated against it (Figs. 1 and 2). Late Cretaceous–

                                                                                               Paleocene magmatic rocks in Idaho and Montana, of which the

                                                                                               Idaho and Boulder batholiths are examples, continue north of the

                                                                                               zone but display a sinistral step before continuing farther north-

                                                                                               ward through the High Cascades and the Coast plutonic complex

                                                                                               of British Columbia (Fig. 1).

                                                                                               Following the same trends as the plutonic rocks is the promi-

                                                                                               nent left step in the initial Sr isopleths of Late Cretaceous–

                                                                                               Paleocene rocks (Armstrong et al., 1977; Fleck and Criss, 1985).

                                                                                               A few plutons of a 100–80 Ma plutonic belt—interpreted farther

                                                                                               south as slab-failure plutons related to the 100 Ma Oregonian

                                                                                               event (Hildebrand and Whalen, 2014)—occur within the Idaho

                                                                                               batholith and to the west in the Cascades and Coast plutonic

                                                                                               complex north of the zone. Eocene magmatism and core

                           Figure 2. Simplified map showing many of the main Cordilleran elements complexes (Foster et al., 2007) also display a sinistral separation
                           discussed in the text. Rotation of Colorado Plateau from Kent and Witte across the zone (Fig. 1), whereas three other Cenozoic groups of

                           (1993).                                                             rocks—dikes and lavas of the Columbia River Basalt Group

                                                                                               (Reidel et al., 2013), volcanic and sedimentary rocks of the

                           transcurrent. For example, it was obvious that, in addition to the  Ancestral Cascades (du Bray and John, 2011), and dominantly
                           thrust belt, the Neogene Basin and Range structural province        basaltic rocks of Siletzia (Wells et al., 2014)—all abut northward
                           occurs much farther west, north of the lineament, than its equiva-  against the zone (Figs. 1 and 2). The classic Laramide basement
                           lent in Mexico (Fig. 1), yet I knew that it couldn’t be a younger   uplifts and basins (Fig. 1), characteristic of the central Cordillera,
                           transcurrent fault because 18.8 Ma Peach Spring Tuff (Fig. 1)       are largely confined to the area south of the Lewis & Clark zone
                           crops out in a narrow band from Arizona to near Barstow,            and north of the Texas Lineament (Fig. 1).
                           California (Glazner et al., 1986) and extends unbroken over the
                           trace of the zone.                                                    Based on the absence of sinistral separation across them, rocks
                                                                                               of the Belt Supergroup appear to sit atop the Lewis & Clark trans-
                             Besides the separation of the Basin and Range and the thrust      verse zone, but the zone expresses itself in the overlying Belt rocks
                           belt, many other features display sinistral separation across the   with a linear band of abundant faults, folds, and intense cleavage
                           lineament (Fig. 1): The post-Sevier dynamic basin (as illustrated   (Wallace et al., 1990; Sears, 1988). A conspicuous band of Late
                           by the 80 Ma isopachs), the Laramide belt of porphyry copper        Cretaceous sedimentary rocks located west and south of the
                           deposits (Gilmer et al., 2003), and possibly the Oligocene ignim-   Boulder batholith (Fig. 1) is an order of magnitude thicker, and is
                           brite flare-up (Henry and John, 2013) all show sinistral separa-    stratigraphically quite different, south of the zone than correlative
                           tion. The oldest rocks that show obvious sinistral separation       rocks to the north in the Montana disturbed belt (Wallace et al.,
                           across the zone are the Callovian salt deposits of the Gulf of      1990). Jurassic-Cretaceous rocks of the Tyaughton-Methow basin
                           Mexico (Fig. 1).                                                    (Umhoefer et al., 2002), and those of the Upper Cretaceous
                                                                                               Nanaimo basin on Vancouver Island (Mustard, 1994) do not
                             Features restricted to the region north of the Texas Lineament    continue south of the transverse zone (Fig. 1).
                           include the Colorado Plateau, the Rio Grande rift, the High Plains

                           province, and the Ouachita-Marathon orogen. Features largely        BAJA-BC RESOLVED
                           limited to the region south of the lineament include the Sonoran

GSA TODAY | NOVEMBER 2015  batholith, related porphyry Cu deposits, and the Pinal schist         Several robust and repeatable paleomagnetic studies exist for
                           (Fig. 1).                                                           the region north of the Lewis & Clark zone. I summarize the
                                                                                               results of several, plus an interesting study of leaf fossils that
                             The Rio Grande rift disappears southward into the Mexican         yielded congruent results, in Figure 3. The results are similar, but
                           Basin and Range, whereas the unbroken High Plains just west of

                           the 100th meridian trend southerly into the Mexican Basin and       those from older Cretaceous rocks have slightly larger amounts of
                           Range (Figs. 1 and 2). Paleozoic features, such as the Ouachita-    displacement relative to the craton, largely because North America
                           Marathon fold-thrust belt and strata of the Permian Basin, are      started to move southward at 90 Ma (Kent and Irving, 2010).
                           truncated and do not appear south of the lineament, whereas the
                                                                                                 A breakthrough in our understanding occurred through paleo-

                           much younger Late Cretaceous–Paleocene Sonoran batholith            magnetic study of the Carmacks Group (Fig. 3), which yielded ca.

                           extends northward into Arizona but remains mostly south of the      70 Ma paleopoles indicating 1950 ± 600 km northward translation
                           lineament and extends westward through the Transverse Ranges,       relative to cratonic North America (Enkin et al., 2006a). The
                           where it ends (Fig. 1). The northwesterly tip of the Texas          group is an amalgamation of 72–69 Ma volcanic and sedimentary

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