Many times when I’m hiking out of the canyon I slow down dramatically when I reach the Toroweap Formation. You’d think not, since the grade usually lets up a bit when you reach the gentler slopes typical of the Toroweap, but you are getting up into thinner air near the top of the canyon, with the Toroweap just the second formation down from the rim. Thin air and a heavy pack near the end of a long climb don’t play well together.
Another thing surprises me about the Toroweap when I’m hiking in. You’d think that you’d get the best vistas when hiking through steeper formations like the Kaibab Limestone above it or the Coconino Sandstone below, but on many trails the views down into the canyon are the best in the Toroweap of any of the upper canyon formations. My guess is that for some reason, maybe the soil, trees don’t like the Toroweap. Trees are abundant above the Toroweap in the Kaibab Limestone, but meadows seem to be the preferred vegetation on the Toroweap. On many trails you dive into the trees as you come off the rim in the Kaibab Limestone, the North Kaibab, Tanner, and New Hance trails are good examples, and the views open up only when you reach the Toroweap.Here‘s part of the expansive view from near the top of the Toroweap Formation on the Tanner Trail. You can see the gentler slopes of the Toroweap sandwiched between the Kaibab and the Coconino. Do note, however, the thin cliff band within and near the bottom of the Toroweap. The Toroweap was deposited about 273 million years ago when the area was on the edge of a warm, shallow sea that sometimes would invade and cover the area, and sometimes recede and leave the area as shoreline land. The narrow cliff band you see here within the Toroweap is limestone, deposited when the sea was present for a relatively long time. Sandstone was formed from dunes when the sea retreated. You will also find gypsum in the mix of many layers that form the Toroweap.
It is usually pretty easy to recognize the boundary between the Toroweap above and the Coconino below. The many layers that make up the Toroweap were all laid down perfectly horizontally, while the Coconino has intersecting cross-bedded layers. If you see a bunch of flat layers in the rocks around you then you are in the Toroweap and not the Coconino. The boundary between the Toroweap and the Kaibab Limestone above it can be harder to distinguish, but the pattern is that the Kaibab tends to be grayish orange, while the Toroweap tends to be light gray. If you see some rocks that are a fairly bright reddish orange near the boundary, however, those rocks are part of the Toroweap.Things change for the Toroweap when you head further west within the park. There the intervals of time when the sea that formed the Toroweap covered the land were much longer, and the bands of limestone deposited in the sea were much thicker. Here we are on the Jim Hall Trail, at a traverse through the Toroweap of about half a mile that the trail follows until it reaches a break in the formidable Toroweap limestone cliff that you can see just below the trail. In a some places the Toroweap slopes disappear and it becomes an unbroken sheer cliff. Here we are looking at the wall of the Desert Facade from across the Colorado at the Anasazi Granary at the end of the Nankoweap Trail. The Desert Facade, along with the Palisades of the Desert, form the massive, sheer eastern wall of the Grand Canyon. The Toroweap here is just another part of that 3000 foot high wall containing seven different formations.
To read more detailed geological information about the Toroweap Formation, visit its United States Geological Service page.