Batholith

Armstrong and others (1977) called the northern part of the hourglass the "Bitterroot" lobe and the southern part the "Atlanta" lobe. He also proposed that most of the southern lobe was emplaced 75 to 100 million years ago (Late Cretaceous); whereas the northern lobe was emplaced 70 to 80 million years ago. Armstrong (1977) further noted that older plutons of Jurassic age occur on the northwest side of the Bitterroot lobe and many Eocene plutons have intruded the eastern side of the Atlanta lobe of the batholith. On the western side of the batholith, there are more mafic plutons (quartz diorites or tonalites) than to the east.
Radiometric dates and field relationships, where plutons of the batholith cut older rocks, restrict the age of the Idaho Batholith to an interval between 180 million years ago (Late Triassic) to 45 million years ago (Eocene); however, the dominant interval of emplacement was Early to Middle Cretaceous. There is a general west-to-east decrease in age for plutons of the batholith.

valcano

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volcanoes are amazing.  they create and destroy, they grow and they fall.  they even erupt in three different ways.  explosions, dome building, and spire making.  it all depends on how much water is in the lava.  the heat turns the water into gas which sends the lava up and out of the volcano.
I learned  a lot of this on channel two last night when some geologists were talking about Mt. Saint Helens. it had all of the different eruptions that i listed above.  first in 1980, Mt. Saint Helens blew up leaving the legendary crater in its surface.  watching Saint Helens blow up in three different spots looked like three missiles hit it.  Saint Helens erupted again in 1983, this time it started dome building.  the mountain would slowly ooze black sticky lava that built the dome,  after a while it just stopped.  finally, in 2004,  it erupted again by making spires.  the spires then crumbled and started again.  the spires stopped 3 years ago.