Sometimes Smart Guides has a difficult time snapping to angles if you start drawing a line without attaching it to an anchor. One thing that you can do is define the angle using the line dialog. The other may be to draw a boundary line at the margin of the cross section. Or, they just won't snap... and I have no idea why. The Mac version of Illustrator seems rather inconsistent with its functions, at times.
But once you get past that initial point of setting up a line, Smart Guides is usually content snapping between lines that represent dip domains (angles that bisect between dip domains). Remember, by default, smart guide activity is symbolized with a green line.
Once you've balanced a cross section, use the measure tool to make sure bed thicknesses and angles come out as expected. It's pretty slick stuff.
|30 and 60 degree angles automatically snapped between bisectors of dip domains.|
So much for the protractor.