Windfall Lake

Most of the rocks encountered along the route are from the Mississippian Period (359-323 million years ago). In some other parts of the world rocks of this age contain the remains of ancient forests, and have yielded abundant coal resources. By contrast, rocks of this age in the Tumbler Ridge area were formed from sediments deposited on the floor of a balmy, shallow sea, about 20˚ north of the equator, off the shore of the continent of Laurentia (North American Craton).  These limestone rocks are from the Rundle Group – initially described on Mt Rundle near Banff, Alberta.

The limestone rocks preserve the remains of the creatures that inhabited this offshore sea. We find trilobites, brachiopods, crinoids, blastoids, ammonoids, bivalves, bryozoans, and a variety of invertebrate burrows. The easiest fossils to recognize are the corals, both the solitary (rugose) and colonial (tabulate) forms. These types of corals went extinct at the end of the Permian Period. Some of these can be seen beside the trail near the south-eastern shore of the lake. Please do not remove them, but leave them for others to enjoy.

The darker cliffs that form the cirque head-wall behind the lake are composed of sandstone rocks from the Triassic Period (252-201 million years ago). They are from the Sulphur Mountain Formation, also described first form the vicinity of Banff, Alberta. As these cliffs are eroded, rocks tumble down the steep and create extensive talus (scree) slopes below. These slopes are incised by steep, dark-walled gullies.

At this time the super-continent Pangaea, surrounded by a super-ocean, was beginning to break up. These sediments were formed offshore, in seas which contained the survivors of the end-Permian mass-extinction event (the “Day-after” fauna). Rocks of similar age and type are today found in such diverse places as Madagascar, Greenland, Spitzbergen, Switzerland and Australia.

The junction between the lighter Mississippian limestone rocks and the darker  Triassic sandstone rocks can be seen in many areas on the slopes and cliffs above the route. The geology is complex, and there are many good examples of rock tilting and folding. In places this is so extensive that the younger Triassic rocks lie beneath the older Mississippian rocks.

But common to all these contact zone areas is the fact that their rocks differ in age by about 69 million years. In other words, the Permian Period (322-253 years ago) is hardly represented at all – this is known as a disconformity. During this whole period there was either limited deposition of sediments, or else they were subsequently eroded.

The waters of Windfall Lake warm up in late summer and may offer a nice swimming opportunity. In early summer sliding down the snowfields into the recently-melted waters of the lake provides a more bracing experience. Look for ducks on the lake surface – Barrow’s Goldeneye is usually the most common species.

The trail passes the outflow of the lake. Just a couple of metres after leaving the lake these waters disappear underground, and emerge much lower down in the valley floor. This is a typical feature of  limestone terrain.

Above Windfall Lake the Circular Route passes through another bowl, with a small lakelet at the bottom which is lined on one side by limestone cliffs. This bowl is enclosed by slopes on all sides, and is known as a polje. All drainage from this lakelet occurs underground.

The easiest “beyond Windfall Lake” destination is the ridge and rounded summit to the south – this is moderate ascent offers fine views, and leads past some of the caves and an interesting sinkhole.

Ascending Mt Crum, the highest summit in the area, is very rewarding, but is a challenging excursion. “Climbing through the mountain” to the top of Tunnel Mountain can just be done in a long day-trip from the trailhead, but is better attempted as an overnight trip, camping near the lake.

Ascending up a steep slope of green vegetation and scree to the top of the ridge behind (west of) the lake and then following the narrow ridge top to gain the high, rounded, unnamed summit at its southeastern end is also feasible. This rewarding excursion offers outstanding wilderness mountain scenery.