At long last I am going to attempt to put something in the adventures section of this website :). My biggest challenge here is that I tend to focus on my adventures too much while they happen, with the result that I completely forget to take photographs or document anything(!). However, that is a pretty lame excuse, so – with the help of the photos of friends – here goes nothin'!
This past December I was in Arizona for the holidays. Often this is a crazy time spent shuttling back and forth between families and friends. This year, however, we combined some family/friend action with a few fun local desert hikes, two of which are the subject of this adventure :).
This past December I was in Arizona for the holidays. Often this is a crazy time spent shuttling back and forth between families and friends. This year, however, we combined some family/friend action with a few fun local desert hikes, two of which are the subject of this adventure :).
The first hike was in the Sabino Canyon area, my old stomping ground. We hiked out to Seven Falls in Bear Canyon just to the east of Sabino. This is about a nine-mile hike ending at a series of vertically arranged pools, or “potholes”, that are apparently caused by erosion with sandy, swirling water. As a kid this was the hike to do when it was super hot out – the only danger of course being that there may not be any water! These pools are reasonably ephemeral and sourced from mountain water run-off, SO dry year = nine-mile hike to hot rocks!
Bear Canyon (and Sabino Canyon as well) were produced by erosion into the metamorphic core complex that makes up the center (core) of the Santa Catalina Mountains north of Tucson. These core complexes result from crustal extension (pulling apart) and have three main parts:
1) an upper plate that is fractured and blocky because of brittle deformation (like what happens if you tried to pull apart something coldish and solid like a stale cookie)
2) a lower plate that is stretched and folded because of more plastic deformation (like what happens if you tried to pull apart something warmish and solid like taffy)
3) a near-horizontal detachment fault separating the two. This fault is the plane of movement where the upper and lower plates were pulled apart from each other.
In this area, extensional faulting (also called normal faulting) took place about 20-30 million years ago (during the Oligocene and lower Miocene Epochs of the Cenozoic Era).
Bear Canyon (and Sabino Canyon as well) were produced by erosion into the metamorphic core complex that makes up the center (core) of the Santa Catalina Mountains north of Tucson. These core complexes result from crustal extension (pulling apart) and have three main parts:
1) an upper plate that is fractured and blocky because of brittle deformation (like what happens if you tried to pull apart something coldish and solid like a stale cookie)
2) a lower plate that is stretched and folded because of more plastic deformation (like what happens if you tried to pull apart something warmish and solid like taffy)
3) a near-horizontal detachment fault separating the two. This fault is the plane of movement where the upper and lower plates were pulled apart from each other.
In this area, extensional faulting (also called normal faulting) took place about 20-30 million years ago (during the Oligocene and lower Miocene Epochs of the Cenozoic Era).
As you walk through Bear Canyon towards Seven Falls, basically you are looking at plastically deformed and metamorphosed rocks in this lower plate – primarily the beautifully banded gneisses from the Catalina Gneiss Formation. The banding could be caused by a few different processes, but essentially reflects the segregation of the darker more mafic minerals (like amphibole and micas) from the lighter more felsic minerals (like quartz and feldspar). In many cases the rocks continued to be deformed after the bands were produced, so you can see some wacky folding of the bands.
This sort of thing is a great reminder of how absolutely INSANE mountain building is. You are basically taking huge amounts of once flat-lying rocks and shoving them kilometers up in the air! And not only that, but while you are shoving them up in the air, they are heating up and under such intense pressure that you can actually cause them to FOLD. And not just some tilting either - totally waved out and bending back on themselves like if you looked at a cross-section of your laundry. Can you even imagine how much force you would have to put on a ROCK to make it fold like your laundry?! Crazy cool – mind blown.
I think I may need to ruminate on how awesome this is for a bit before I tell you about the wicked caldera collapse we saw when hiking through the “Tucson Mountain Chaos” on our second adventure to Wasson Peak :).
This sort of thing is a great reminder of how absolutely INSANE mountain building is. You are basically taking huge amounts of once flat-lying rocks and shoving them kilometers up in the air! And not only that, but while you are shoving them up in the air, they are heating up and under such intense pressure that you can actually cause them to FOLD. And not just some tilting either - totally waved out and bending back on themselves like if you looked at a cross-section of your laundry. Can you even imagine how much force you would have to put on a ROCK to make it fold like your laundry?! Crazy cool – mind blown.
I think I may need to ruminate on how awesome this is for a bit before I tell you about the wicked caldera collapse we saw when hiking through the “Tucson Mountain Chaos” on our second adventure to Wasson Peak :).