Acronym for remembering the ideal anchor location. Let's go over what each letter means.
This is canyoneering. Canyoneers descend canyons. Canyons are formed by water and in particular flash floods. Flash floods destroy everything, including anchors. We want our anchors away from water as much as possible.
For bolts we want them to be out of the main drainage where we walk. They should be high up enough that they don't get hit often with flood waters. We also want them out of any drainages coming from above. You can usually tell where streams come down by their discoloration compared with the rest of the wall.
We want it to be as close to the drop as possible. If we have a choice between a large natural anchor right next to the rappel and a large natural anchor 50 feet away from the rappel we should choose the large natural anchor right next to the rappel.
Other things that would be efficient would be to avoid places with lots of loose rocks that would be a hazard for canyoneers down below. We should also avoid cryptobiotic soil, bee hives, or other potential hazards.
This one is often counter to many of the other priorities already outlined above. The anchor location should minimize friction when pulling down the rope. This often means compromising between this and accessibility or efficiency.
To solve the problem of inefficient anchors, tough rappel starts, and difficult rope retrievals we use courtesy rigging.
See my article on The Pull for more information on rope retrieval.
The final rappel in Behunin Canyon has two or three bolts with chains attached to them. There are chain grooves in the rock that I presume are from flash floods tossing the chains around. Mostly Dry but not always, Efficient, Accessible, good Rope Retrieval.
The Mystery Springs rappel in Mystery Canyon has an exposed traverse to get to the rappel anchors. However the rope retrieval is much simpler and avoids a huge chockstone. Dry, Efficient, not very Accessible, but good Rope Retrieval.
The final rappel in Zero Gravity Canyon used to be a chockstone above a Mae West slot. Canyoneers would rig and then have to traverse horizontally to where the canyon bottom opened enough to fit through. The canyoneer would basically down climb until they fell and then swing back. Now there is at least one bolt that Search and Rescue uses so this R-rated rappel isn't necessary anymore. It used to be Dry, not very Efficient, not very Accessible, and good Rope Retrieval. Now it is DEAR but not nearly as fun.
The big rappel in Lomatium Canyon has has three different anchors since I first descended it. We used to rappel from Abbey Arch but Arches National Park put a policy in place that said rappelling from arches was no longer allowed. Consequently the new anchor was a skinny tree about 50 feet back from the rappel. This was inefficient, had a difficult pull, and was killing the tree. There was some discussion about it and some considerate canyoneers and park rangers went and installed some bolts closer to the edge. It is now in a DEAR location.
There are two noteworthy rappels in Spry Canyon.
The first one is about half way through the canyon. In order to reach the pair of bolts and webbing one has to lean over a cliff to the opposing wall where the bolts are located. It's something I would do without a second thought if there weren't a huge hole below me but in this circumstance I always go slowly. Dry, Efficient, not very Accessible, great Rope Retrieval.
The second one is closer to the end of the narrows. It uses a large tree as its anchor. The webbing used to be tied in a redundant wrap at the base of the tree. This, however, has led to some of the worst rope grooves I have ever seen. Great location except for the horrible rope retrieval. More recently the webbing was changed to a wrap 3 pull 2 higher up in the tree. This simple change fixed the rope groove problem as well as improved the pull. Perfectly DEAR now.