Here's a close-up of FOUR log cabin modules (two in green, one in black, one in blue)
Log cabin knitting is a form of modular knitting, usually done in garter stitch only, and ideally done in well-matched colors. But this is also a way to use up scrap yarn.
As with most things involving knitting, I relied primarily on online research to learn log cabin knitting. I have yet to get THE bible on log cabin knitting, Mason-Dixon knitting.I adapted the concept to come up with a placemat in acrylic and a bathroom mat in cotton yarn.
Here are a few helpful links on log cabin knitting.
You'll have to scroll down a bit for the blog post, "This Old Log Cabin," by one of the authors of Mason-Dixon knitting.
A mathematical formula on making your own log cabin pattern: How to Build a Log Cabin
Pattern for a log cabin scrap blanket
There are also video tutorials on how to do the joins in log cabin knitting. I actually enjoy this part, as the garter stitch can get boring and the joining/changing to a new color gets your attention :-)
