Down a 7.5 Minute Rabbit Hole

My inbox has quite a mix of fanciful tidbits, futuristic sciences, farming inventions, life hacks, folktales and predictions. Of the wild mixture I find the monthly newsletter from DNR Washington (Department of Natural Resources) always a fascinating read and many times it becomes fodder for me to further investigate what they publish to see if Oregon has the same technology posted. Recently I found the interesting LIDAR research of the Pacific Northwest.

The map area includes the Tenalquot Prairie quadrangle and the northern two thirds of the Vail quadrangle in Washington’s southern Puget Lowland. This map supports private and public resource management with insights into geologic deposits, structures, and hazards. Based on 59 new whole rock analyses, all igneous rocks in the map area are from the Northcraft Formation. Eight new radiometric ages between 45.8 ±0.07 Ma and <38.4 ±0.5 Ma establish this unit as the oldest known expression of Cascade arc magmatism. These ages also indicate that Cascade volcanism overlapped the waning stages of Siletzia volcanism.

Preliminary analysis of aeromagnetic and gravity potential fields suggests that the Olympia geophysical lineament results from a normal fault and the Tacoma basin northeast of it contains a significant thickness of shallow igneous rocks that likely are Northcraft Formation. If both are true, then the Olympia fault has experienced no major northeast-down movement since the end of Northcraft Formation volcanism—which our age control suggests may be entirely middle Eocene in the map area.

Vashon glacial sediments, especially outwash, provide productive but easily polluted aquifers for private water wells and the cities of Yelm and Olympia. The extensive outwash gravel terraces in Tenalquot Prairie and the Deschutes River valley also host widespread, enigmatic Mima mounds. Lacustrine sand above outwash gravel and moraine deposits between Tenalquot Prairie and Lake Saint Clair suggest that large outwash channels were somehow later submerged by an ice-dammed lake with a shoreline at 400 ft elevation. Terminal moraines from the eastern (Yelm) and western (Olympia) ice lobes appear as hummocky glacial sediments east, north, and west of Tenalquot Prairie and along the hill front south of the Deschutes River, suggesting Vashon ice did not override Tenalquot Prairie. Heavily weathered pre-Vashon Drift extends miles farther south in this area but approximates the Vashon ice limit farther east and west. Bouldery outwash trains and denuded bedrock surfaces in the valleys of Johnson Creek and the Skookumchuck River document massive proglacial meltwater discharge south of all known ice limits.

The new LIDAR technology can bring history to a clear light and has improved greatly over the last couple of years. Here in Oregon the LIDAR maps are also available through the help of DOGAMI (Department Of Geology and Mineral Industries) Imagery.

Each 7.5 minute quadrangle gives intense views of the area in both highest hillside hit (able to show individual trees, buildings and even vehicles during LIDAR scan) and bare earth hillside shade (can show varying levels of the landscape to view each ridge along with exact height above sea level.

I still haven’t found images of my area that are in the amount of detail that I found in the Washington DNR site and will have to wade through a few more rabbit holes to find more information.

I’m sure that the dark days and early evening of wintertime are made for just such research.