How far into a footing pier should rebar extend from the rock below?
Well, if it's poured &amp; done, you're evidently into the test phase, so this is not really going to help you much unless it fails and you replace it (which seems unlikely.)
Normally you want rebar a few (2-3, depending on conditions) inches deep in the concrete (for corrosion resistance) but otherwise as near the edges as practical, and connected to as much of the mass as practical.
The basic spacing sounds reasonable, but the fact that it's all within the footing is less than optimal for the pier. There are probably few tension loads on the pier, so it's likely to be fine - you've got the footing attached to the bedrock.
Normally you also want to &quot;cage&quot; between your uprights - tying the bent-over bars in the middle is probably doing the least they can do for you, but you didn't cut them long enough to bend over and reach the next corner, and you don't mention bending and tying any other rebar in that position, or adding mesh. Whether doing a single pour or two pours, it's good practice to have rebar sticking up from the base into the pier, though your pier is rather short. So having it stick up 4&quot; when the pier starts at 5 inches and tops out at 9 inches is less than ideal.
When anchoring to rock, I prefer to drill at slight angles so the rods cannot be pulled straight out as a set once the concrete is poured, regardless of epoxy or grout holding them in the holes.