![]() This Quiburis outcrop is a southwestern distall tip of one of Soza Mesa's many outstretching fingers. (See also More Recent Formations.)īelow, a photograph of Henderson Cliffs on the right bank of lower Hot Springs Canyon in February 2008. Most of Soza Mesa, for example, is composed of this formation - it is the remnant of a great alluvial fan (bajada) built from debris eroding out of the Galiuros when they were much higher in elevation. These sedimentary rock strata lie in a characteristically very gradual slope, at the tilt of their original deposition. These are the most recent of the older Cenozoic (Tertiary Period) formations in the canyon, and are called the Quiburis Formation (massive beds of fairly fine alluvium deposited in the San Pedro basin trough from sources in the great Galiuro fault-block mountains to the east, during late Miocene to early Pliocene times, about 7 to 5 million years ago). (For map orientation, see Hot Springs Canyon Map.) The Quiburis and San Manuel Formationsįirst, beginning well downstream from the Windmill, one sees fairly smooth, vertical-sided, reddish-brown walls of pebble-to-cobble conglomerate sediments, high up on the flanks. Rocks in the alluvium: Two characteristic cliff formations flank both sides of the lower canyon at and near the Rabbit Ears Saguaro Hill. The widely separated canyon walls present a different appearance from these black These large river cobbles are common in our Hot Springs Canyon floodplains because basalt is composed of tightly interlocking crystals that resist the poundings of waterflow, hence the rocks retain their coherence over long distances as they are gradually borne downstream. These are basalt rocks eroded from a lava flow some millions of years ago the remains of which are found far to the northeast of our area, on the east side of the East Range of the Galiuros (see Galiuro Mountains), near the headwaters of Bass Creek (a major tributary of Hot Springs Canyon), located to the south of Bassett Peak. These have eroded from diverse rock formations located upstream.įor example, at left, consider one of the many blackish, rounded river cobbles, some quite large, each densely vesicular (filled with many small holes, formed by gases contained in the volcanic magma as it cooled). Note the wide variety of cobble-to-boulder water-worn clasts lying scattered amidst the sands and silts of the floodplain. As you go up the Hot Springs Wash from the Windmill toward the Rabbit Ears Saguaro Hill (and our deeded land fence and gate), you walk along the low silty and gravelly terraces of the floodplain, which is stream alluvium being deposited during Pleistocene to recent times (the Quaternary Period, here much less than 1 million years old).
0 Comments
Leave a Reply. |