Origami Mountain Fold
In origami, a Mountain Fold is shown with a “dash-dot-dot; dash-dot-dot” line and an open (white), half arrowhead. Some authors use a “dash-dot” line instead, and there is much variation in the arrowhead.
The dash-dot-dot line indicates where the paper folds and the arrow shows directionality (fold behind and upwards).
Origami Mountain Fold Instructions
In this example, the fold is made by folding the bottom edge behind the paper and away from you.
If you were to unfold this, you would find a crease line at the exact location as the dash-dot-dot line.
John Smith has developed a branch of origami called Pureland Origami. In pureland origami, only valley and mountain folds are used.
In practice, it is often difficult to fold a sheet of paper behind and away from you because you cannot see under the layers of paper. Instead, most people do the following:
1) turn paper over
2) make a valley fold
3) turn paper back over again.
As you can see, the result below (f) is effectively the same as above. Mountain and valley folds are similar: one folds to the front while the other folds to the back.