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The National Gallery in London is not merely a repository for what appears to be a large potion of the oeuvre of the old masters. It also has a vast collection of the "new" masters of impressionism and onwards, whom I won't bother to rattle off. Perhaps fewer, since, being newer, other museums had more of a bite at the apple of such works before Mother England could suck them all into her gravitational maw. I like the high impressionists and pointillists as much as the next guy, but I have a particular fondness for Degas, and it was there that I found Lonnie, eschewing the medley of Monets and Manets across the room.
The pair in question are only modestly well known, perhaps -- Peasant Women Bathing in the Sea at Dusk of 1875, and Young Spartans Exercising of 1860. But I have always thought both are remarkable pieces. Peasant Women is perhaps a more classically Degas treatment, suggestive and a bit dreamy and in their linked hands in choreographed movement, invoking Degas's more traditional ballet studies whilst entering into new territory of theme and technique. Young Spartans, on the other hand, is a rather rare subject, but captures the fragility of adolescent psyche and vulnerability to mockery and judgment that will be familiar to anyone who was in high school, as a gaggle of dressed adults stand impassive and oblivious in the background to the boys' and girls' frolicking, fighting or flirting.
FIELD GUIDE TO "A" MOUNTAIN AND DESCRIPTION OF SURROUNDING REGION
by
Thomas G. McGarvin
ARIZONA GEOLOGICAL SURVEY
I have heard that this hill was called Dynamite Hill by a longtime Tucson resident.
The Geology of “A” Mountain
If you drive up Sentinel Peak Road, you will travel past a series of rock layers that formed between twenty and thirty million years ago. These multicolored strata produce the bedrock that constitutes “A” Mountain as well as the nearby Tumamoc and Powder House Hills. These hills and “A” Mountain are the visible remains of a former landlocked peninsula that was anchored in the west by the Tucson Mountains and extended beyond the present day Santa Cruz River to the east. “A” Mountain is an erosional remnant of this land prominence sculpted by the forces of ice, wind and water. Four distinct and interesting rock layers are easily visible on the face of this 550-foot mountain.
Flowing lava created the dark red rock strata at both the top and the bottom of “A” Mountain. Nearby volcanic pipes and fractures supplied the basaltic magma that created these beds, each one separated by a span of nine million years from the formation of the other. None of this lava came from the large “volcano like” crater on the northeast side of the mountain. Quarrymen from the Griffith Construction Company dug this basin at the turn of last century in the pursuit of its stone, used for building Tucson homes, walls and other structures.
The dark red color of these two basalt layers is due to a high concentration of iron and magnesium in the original magma. These elements reduce the lava’s viscosity and the explosive tendency of the sourcing eruptions while allowing the molten rock to flow more uniformly across the surface. Much of the basalt layer at the base of “A” Mountain contains small cavities known as vesicles. The magma, in this case, erupted out of the ground just fast enough for the dissolved gasses to vaporize in the decompressing molten rock and then cooled fast enough to retain the holes formed by these gas pockets. The same bubble forming principle occurs when opening a bottle of beer. An example of this vesiculated basalt is visible on the west side of Sentinel Peak Road between the parking lot at the bottom and the beginning of the one-way road around the summit. The basalt cavities are at the top of this dark layer, presumably because the bubbles floated upward before the cooling lava locked them in place.
The two rock layers sandwiched between the basalts were the result of more violent volcanic activity about 27 million years ago. The older of these two light colored rock strata is composed of rough dark pebble size cinders (basalt) embedded in silt, sand and ash. This material fell from the sky in the form of a volcanic cinder fall. The light brown agglomerate layer with its dark embedded pebbles is visible on the left side of the one-way lane just beyond the split in the road.
Finally, the most visually striking layer of “A” Mountain is composed of tan and pink rock, known as tuff. This layer resulted from one or more volcanic ash falls. The magma for this ash also went through decompression near the earth’s surface. In this case, however, the eruption occurred so suddenly that the expanding gas in the magma shattered the molten minerals and rock into very fine pieces and threw them forcefully into the air. After settling back to the ground, the combination of heat, pressure and time welded this bed of ash into the light colored rock layer that we can see today. Look for a sharp color transition between the tan rock and pink rock as you drive up the southern slope of “A” Mountain. This will identify the tuff layer that is also visible as a large light horizontal bed on Tumamoc Hill to the west.
This introduction to the geology of “A” Mountain is an invitation to explore and enjoy our hilly community with an understanding of its primordial past. The vestige of this beginning is locked within every pebble and stone of our iconic mountain.