Carnegie - the debris flow volcano
Carnegie is the prominent peak on the north-eastern crest of Volcan Santa Clara, just slightly lower (77 m) than nearby Pinacate Peak. Its eruption forty-odd thousand years ago produced a pyroclastic cone with a major debris flow, four lava flows, and a widespread cinder blanket. The peak was named for Andrew Carnegie, benefactor of the Carnegie Desert Laboratory in Tucson where the 1907 Hornaday expedition to Pinacate originated (Hornaday, 1908, Campfires on Desert and Lava).
The cone is asymmetrical having a high southern part with the peak and a lower northern part that contributed to the debris flow. Four lava flows are associated with Carnegie; the two on the west are unremarkable but the two on the east formed spectacular lava falls and both reached the desert floor 12 km from the cone. The Santa Clara summit platform and much of its upper slopes are covered with a cinder blanket that appears to have come from Carnegie. Nonetheless, the cone is made of welded scoria not of cinder.
Carnegie cone
Carnegie sits upon the landscape having a smooth, angle-of-repose slope that intersects the land surface at a sharp angle for most of its circumference. The cone as seen in the gallery of aerial oblique images and (link to GE) appears to consist of two parts. On the south is an intact half-cone with the peak; on the north is a broken half-cone that fed the debris flow down the flank of Santa Clara.All the views of the summit area show the cinder blanket over everything. Cinder so nearly hides some of the lavas that they are only visible in the right lighting conditions - like the flow in the lower right corner of the header image. Cinder has been reworked by runoff since the eruption. This FlashEarth snapshot shows removal of cinder that fell into a breached cone. The West lava flow on the right in this view is partially covered by reworked cinder.
Where the rock came out
A large volume of flow basalt is associated with the Carnegie eruption; two old and two young, two west and two east. The old flows are "gray" basalts that have some airfall cinder; the young flows are black-brown basalts that have alluvial cinder. The flows that are black in satellite images (link) and take on a red-brown desert varnish can be traced to three sources; the western base of the cone, the eastern base of the cone, and the wall of Lava Canyon on the S80E strike of the fissure. Hornitoes covered with pahoehoe spatter were built on both ends of this east side fissure. On the west, lava came out near, but not at, the base of the cone directly beneath a major concavity in the cone slope. Basalt there is two streams separated by a "loaf-shaped" mound of scoria 100 m across and 350 m long that might have been part of the cone wall. Pahoehoe-like slab surface is found on the western flow in several places.The poor color of this FlashEarth image accentuates the difference between the black and gray lavas on the East Flank.
Lava flows
Black and gray flows on the northeast flank of Santa Clara may not both be from Carnegie. The dark material without air-fall cinder clearly came from the fissure at the base of the cone at Iitoii's Cave. The cinder covered lava levees and basalt under this material cannot be traced to a vent but a possibility exists that this flow was coming down the mountain before the cone was built and it initiated the debris flow collapse. The contact btween this older basalt and the debris is buried.The distinct color difference between the black and gray basalt is obvious in all of these images. Even the too-light FlashEarth imagery retains the difference.