This field trip route leaves Grand Canyon National Park entirely (Figure 1.1 in FIELD GUIDE TO THE GEOLOGY OF THE SOUTH RIM), heading south on AZ Hwy 64 to Red Butte, an isolated knob of rock preserving just a tiny smidgen of Mesozoic sedimentary rocks capped by resistant Tertiary basaltic lavas and offering a spectacular 360º panoramic view from a fire tower perched on its summit. The hike to the top of Red Butte is a comparatively easy stroll (when stacked up against your average trek in the Grand Canyon) of only about two and one-half miles round trip through a pleasant stretch of pinyon-juniper forest. On your climb, several outcrops provide an extremely rare opportunity to view Triassic age Moenkopi and Chinle Formation sedimentary rocks, as well as the basaltic lavas capping the butte. From the top, the surrounding Kaibab Plateau rises gently to the northeast, while the more distant mountains of the San Francisco Volcanic Field lay to the south.
On your drive to the base of Red Butte, you cross Kaibab Limestone, the resistant, Late Permian sedimentary rock that comprises the uppermost Paleozoic “bathtub ring” within the confines of the Grand Canyon, as well as virtually all of the material capping the North and South Rim plateaus. It may seem hard to believe, but that rock unit was not the last to be deposited in the Grand Canyon region; in fact, as much as 4000 feet of Mesozoic sedimentary rock once covered the area, only to be removed by pervasive lateral stripping of the strata during the warm, moist conditions of the early Tertiary, leaving the dense Kaibab Limestone to buttress the canyon rims. Geologists know that Mesozoic sedimentary rocks once blanketed the region from thick sequences left behind to the north and east, and from sparse clues like those of Red Butte (and Cedar Mountain near Desert View) preserved on the Kaibab Plateau itself. Erosion would have removed Red Butte’s Mesozoic rocks if a resistant lava flow from the San Francisco Peaks to the south had not entombed them. Red Butte itself is so named for the reddish hued, tidal-flat derived mudstones of the Moenkopi Formation that underlie a thin slice of sandstones from the basal Shinarump Member of the Chinle Formation; both rock units representing the Triassic Period of the Mesozoic Era.
The San Francisco Volcanic Field is a collection of several hundred small cinder cones and lava domes interspersed among roughly a dozen larger volcanic peaks. Volcanic eruptions began near Williams, AZ in the Late Tertiary about 9 million years ago, but the center of active volcanism migrated slowly eastward, with the most recent activity generating the cinder cone of Sunset Crater some 900 years ago. Much of the volcanism was basaltic, forming the maze of cinder cones and their associated lava flows that represent the bulk of the San Francisco Volcanic Field, but less commonly, large pods of viscous andesitic and dacitic magma erupted to create large composite volcanoes like Mount Humphreys (San Francisco Mountain), and small lava domes such as Elden Mountain near Flagstaff, AZ. Several eruptions produced copious rivers of basaltic lava that travelled many miles from their source; the lavas capping Red Butte are all that remains of one of the older flows.
0.0 (0.0) Refer to Map 1C.1. Intersection of Grand Canyon National Park entrance road (U.S. Hwy 180) and Desert View Drive (AZ Hwy 64). Head south onto U.S. Hwy 180 toward the park entrance.
1.3 (1.3) Intersection of Grand Canyon National Park entrance road (U.S. Hwy 180) and Center Road. Continue south onto U.S. Hwy 180 toward the park entrance. Center Road offers an alternate entrance to the Grand Canyon Village area that avoids the traffic congestion around the park’s Visitor Center.
4.3 (3.0) Refer to Map 1C.2. Grand Canyon National Park boundary and entrance station; continue south on US Hwy 180 toward Tusayan.
5.7 (3.0) Round-about at the north end of Tusayan, AZ. The road drops into a small, NE-SW oriented, normal-faulted graben here. Although the structural feature is fairly subtle at this end, it is readily distinguished on Map 1C.3. Rain Tank Wash drains from the southern end of the valley created by the graben and exploits the fault-induced zone of weakness in the Kaibab Limestone trending to the southwest.
6.3 (0.6) Refer to Map 1C.3. Round-about at the south end of Tusayan, AZ. Shortly, the road climbs the southeast flank of the graben.
6.6 (0.3) The northern entrance to Grand Canyon Airport lies on the right-hand (northwest) side of the road; the airport runway follows the axis of the graben to the southwest.
7.2 (0.6) The southern entrance to Grand Canyon Airport lies on the right. From here, U.S. Hwy 180 follows the gently undulating back of the Kaibab Limestone, gradually descending into a topographic basin near Valle, AZ which is floored by red mudstones of the lowermost Mesozoic Moenkopi Formation.
15.0 (7.8) Refer to Map 1C.4. U.S. Hwy 180 passes FS Rd 305 on the left (east). This location offers your first good view of Red Butte lying to the southeast.
16.5 (1.5) FS Rd 347 lies on the right-hand (west) side of the road here. The green-gray “hills” on the horizon are volcanoes of the San Francisco Volcanic Field. In contrast, Red Butte is not a volcano, although it is capped by an erosional remnant of an ancient lava flow originating from those distant volcanoes.
17.8 (1.3) Intersection of U.S. Hwy 180) and FS Rd 320. Turn left (east) onto FS Rd 320. As you proceed, good views of Red Butte’s southwestern flank open up, notice the exposures of red Moenkopi Formation mudstones which provide the isolated knob its name.
18.0 (0.2) FS Rd 320 first ascends a low rise, then drops into a distinctive NE-SW trending swale here, likely controlled by erosion along a fault trace more readily observed on Map 1C.4.
19.2 (1.2) Refer to Map 1C.5. Intersection of FS Rd 320 and FS Rd 340 on the left (north). Turn onto FS Rd 340; great views of Red Butte lay off to your right. Careful observation from here should reveal the butte’s complete stratigraphy which is well exposed in its southwest flank (Figure 1C.1). Slope-forming, red mudstones of the Triassic Moenkopi Formation overlain by a thin, buff-colored, cliff-forming, sandstone of the Triassic Chinle Formation’s basal Shinarump Conglomerate Member form the base, while the summit is capped by much younger, Tertiary age grayish, basaltic lava flows. The lavas provided a resistant cap rock that ultimately preserved this small patch of weaker Mesozoic sedimentary rocks.
Figure 1C.1. Red Butte, observed from the intersection of FS Rd 320 and FS Rd 340; note the red-colored sedimentary rocks (capped by gray basalts) exposed in your near view, perhaps not butte’s name isn’t terribly creative, but it is accurate.
20.1 (0.9) Intersection of FS Rd 340 and FS Rd 340A. Turn right (east) onto FS Rd 340A for the final leg of your drive.
20.5 (0.4) Trailhead parking area for the Red Butte Trail; park anywhere, but please don’t block the road (see the Red Butte Trail – Tr 1C.1 described in the Optional Hiking Trails section of Field Trip 1C). When you return, it’s only a short drive back to the park; but you may wish to make a detour while in Tusayan, AZ for souvenirs and supplies.
Road Route Maps
Map 1C.1. Color shaded-relief map of the Phantom Ranch 7.5” Quadrangle containing segments of Field Trip 1B and Field Trip 1C.
Map 1C.2. Color shaded-relief map of the Tusayan East 7.5” Quadrangle containing segments of Field Trip 1B and Field Trip 1C.
Map 1C.3. Color shaded-relief map of the Tusayan West 7.5” Quadrangle containing a segment of Field Trip 1C.
Map 1C.4. Color shaded-relief map of the Red Butte SW 7.5” Quadrangle containing a segment of Field Trip 1C.
Map 1C.5. Color shaded-relief map of the Red Butte 7.5” Quadrangle containing a segment of Field Trip 1C.