1. Kootenai Falls Field Trip Geology 201, Spring 2009

2. Kootenai Falls Field Trip, Spring 2009
The Spring 2009, Earth Through Time class (Geol201), took a field trip to Kootenai Falls and Yaak Falls to examine sedimentary rocks, structures and fossils of the Proterozoic, Belt Supergroup. We traveled around the north end of Lake Pend Oreille and then on to the Bull River Valley. From there we skirted the western side of the Cabinet Mtns. Wilderness and arrived at beautiful Kootenai Falls on the Kootenai River. After examining abundant and spectacular sedimentary structures & stromatolites (world-class!) at the Falls, we traveled west on Hwy. 2 to the Yaak River & Yaak Falls. We finished the trip looking at spectacular domal stromatolites along Hwy. 2 just west of the Yaak River road.

3. Cabinet Mtns., Bull River Valley

4. Cabinet Mtn.s & Bull River Valley
The Cabinet Mtns. are a small but impressively beautiful range in western Montana. The Cabinets exhibit dramatic exposures of the Belt Supergroup sequence. The Bull River Valley borders the western side of the Cabinet Mnts. Wilderness and is very scenic, especially in early spring when the high Cabinets are covered with snow. Driving along Hwy. 56, you’ll notice numerous exposures of glacial till deposits along your way to Bull Lake. Be sure to take the short drive north (4 miles) to the Giant Cedars Grove and take the short hike.

5. Cabinet Mtns., Bull River Valley

6. Stan, Lindsey, Dominick, Teresa, Wayne, & Ryan

7. Giant Cedars grove , Bull River Valley

8. Bull River Valley, looking east

9. Belt Supergroup
The Belt Supergroup is a thick sequence of Proterozoic-aged sedimentary rocks. The Belt is known for exquisite preservation of sedimentary structures with a variety of bedding types and features. Why do the Belt sediments exhibit such excellent preservation of the sedimentary features? Maybe the next paragraph holds a clue. In general, fossils are very rare within the Belt sequence but there are few localities where evidence of ancient life can be examined, up close and personal. At the Kootenai Falls site, world-class exposures of stromatolites can be viewed and enjoyed. A fantastic setting, some of the oldest fossilized life forms can be studied at Kootenai Falls between Libby and Troy, Montanan, along Hwy. 2.

10. Belt Supergroup
The Belt sequence is comprised of over 18 km of sand, silt, and carbonate sediments that have been weakly metamorphosed. The Belt sediments were laid down ~1.4 billion years ago in an intracratonic basin. As the basin filled, the depositional environments became very shallow and tidal deltas were a predominant feature. These shallow tidal deltas ultimately laid down layer upon layer of sediment often with current-related structures such as ripple marks and cross beds, along with wetting-drying structures such as mud cracks. The Belt is subdivided into four major groups and many formations. From oldest to youngest, the groups include: the Lower Belt Group, Ravalli Group, Middle Belt Carbonate Group, and the Missoula Group. For more info on the Belt, go to Dr. Don Winston’s website:

11. Babbling about the Belt

12. Ripples in the Mt. Shields Formation of the Missoula Group

13. Mudcracks (?) in the Mount Shields, Kootenai Falls

14. Kootenai Falls

15. More great sedimentary structures, Mt. Shields Fm., Kootenai Falls

16. Which way to the stromatolites?

17. World class stromatolites

18. Some of the oldest fossil life forms in the PNW ~1
Some of the oldest fossil life forms in the PNW ~1.4 billion year old stromatolites, Mt. Shields Fm. of the Missoula Group

19. Finely laminated muds and silts, Mt. Shields Fm.

20. Swinging Bridge and stromatolite bearing Mt. Shields Fm.

21. Broad fold in Mt. Shields, Hwy 2 above Swinging Bridge

22. More stromatolites and ripples

23. Yaak Falls & dipping strata of Prichard Fm., Lower Belt Group

24. Upper & lower Yaak Falls

25. Excellent ripples & cracks, Mt. Shields Fm., Missoula Group

26. Domal stromatolites, steeply-dipping Mt. Shields Fm., Hwy. 2

27. The End!