Log Cabin Triangles

Okay, time to fulfill my promise. Here is how to do log cabin-style triangles.
This is the middle, as previously shown.
 

Here is a marked-up version.

All in garter stitch.

The center triangle: cast on 21, and then decrease one stitch at the beginning of each row (decreasing one stitch on each side for each ridge), until down to 3 stitches, and then knit through all 3 and bind off. This makes a triangle with 45 degrees angles at the bottom, and a 90 degree angle at the top.

Section A: Pick up along one side of the triangle, picking up 7 stitches for each 5 ridges. Knit back and forth, increasing one stitch in each ridge on the side towards the bottom (hypotenuse) of the triangle. (I increased one on the right side, then just knit back for each ridge.)

(I'm traveling, so I don't have this in front of me, but I'm guessing I did ten ridges? it doesn't really matter, pick whatever looks good to you.)

Section B: Pick up along the side of section A, picking up one stitch for each ridge, and then down the side of the triangle, picking up 7 stitches for each 5 ridges. Knit the same way as A, increasing one stitch in each ridge on the hypotenuse side.

Section C: Pick up one stitch for each ridge along the side of Section B, pick up along the bottom of the triangle, stitch for stitch, and then pick up one stitch for each ridge along the side of Section A. Increase one stitch on both sides for each ridge.

This creates a piece with the same angles, 45 -45- 90. You could keep going like this, around and around, and then make another piece the same way, and put them together along the hypotenuse to make a square.

That isn't what I did. Here is how mine now looks.

And here's a closer look. You can see that I made one more layer around the middle before turning it into the top middle of what will be a triangular shawl.