My S.O. and I are both geology nuts and amateur rockhounds. We DVR every mining show on Discovery Channel, and went so far as to purchase a gold pan last year (although we have not yet broken it in). And coincidentally, several months after we began dating, we realized we took the exact same geology class in college before we ever knew one another — quite remarkable, considering our university had an enrollment upwards of 25,000 and neither of us were geology majors. But geology has always been a shared interest.
Several days ago, I attended a Sunset Series lecture through the City of Boise’s Environmental Education Program. Initially I thought this would be a chore — one of several City-sponsored activities I could choose to sit through to get my $100 refund from my homeowners’ association. But the event grabbed the greenhorn geologist in me. It started off with a fascinating 45 minute lecture on the geologic history of Southern Idaho — from the Supercontinent Rodinia through the formation of the Snake River valley. Afterward, we were led on a 1.5 mile hike into the Boise Foothills to identify several of the geologic features from the lecture.
I knew my S.O. would have enjoyed the geology, so I led him on the same hike today. We headed along Lower Hull’s Gulch Trail #29, and barely a quarter-mile east of the Foothills Learning Center, we came across this layered outcropping rich with ancient corals, chunks of granite, and fossilized trees.
These layers of sand are sediments deposited by flow into the ancient Lake Idaho, a massive body of water that covered most of Southwestern Idaho between 2 million and 9 million years ago.
Hull’s Gulch and many of the Boise Foothills formed the ancient shoreline of Lake Idaho. The different colors of sand represent different compositions — the deeper orange sand having higher iron content, and the grey sand containing ash, representing volcanic activity.
Fossilized trees are these small, ruddy pieces embedded in one of the upper layers of sand.
I’ll leave you with a shot of Hull’s Gulch from our elevated viewpoint after climbing up the sandy outcrop.