When descending canyons we often get to a drop that it too difficult to down climb but we need to get down. How are we going to do it? Ladders are too bulky and heavy and don't reach very far. Rope ladders or etriers might work better but you'll need something to anchor it to at the top. And if it's a long distance it might be scary and I'd worry that someone would panic and accidentally let go.
How about we use rope and then each person rappel? Rope is light-weight, the person can easily lock off mid-rappel if the need to. They can easily be belayed from the top or bottom. These advantages are why so many canyons require rappelling to safely descend.
We still need to solve the anchor problem, though. We need something solid at the top to hold the rope and anything loading it. It should be redundant because we might not necessarily be able to trust it. It should be able to survive weather, heat, sunlight, and freezing temperatures. It shouldn't cost too much money if we have to purchase material that we leave behind. Leaving it should not be illegal. It shouldn't be ugly or detract from the natural setting, either.
Everything I know about rocks and trees and how they can be solid rappelling anchors
Equalized Angle Redundant No Extension Solid Timely - The best way to connect webbing to anchors
Dry Efficient Accessible Rope Retrieval - Qualities of an ideal anchor location
Webbing
Flat woven fabric primarily used in rigging. The best canyoneering webbing is tubular and 1" across.
Because webbing is left behind in a canyon, many canyoneering locations require webbing to be specific colors. No location prohibits black webbing so it is always a safe choice.
Same as Tape.
Webbing is tied around anchors and left behind.
These are anchors with multiple pieces of webbing. If I ever get to this I will go through how to make them all meet up at a master point.
Marginal Anchor
An anchor where the amount of force a canyoneer applies to it is close to the amount of force that will cause it to fail.
Transient Anchor
A temporary anchor that is created and used for the rappel and then removed afterwards. Examples are sand trap, water anchor, human anchor, sand bag, pack drag, and hook.
Much bigger topic and definitely intermediate/advanced (everything on this page so far is beginner).
Topics would be cairn, deadman, and meat anchors. Could eventually get to transient anchors.