The range here will be approximate, ideally based on an individuals personal needs, abilities and experience. Your left foot, poised on the heel only , pointing to the West , rests a comfortable distance ahead of, and a few inches to the left side of, your right foot, which is pointing to the NW corner.
Arms make the mountain begins here with the typical, nearly imperceptible, tai chi segue.
As your movement forward is concluding, your arms begin to draw away from each other, by slowly unbending your left arm and slowly bending your right arm. As you pivot , rotate your torso at the waist to your right, turning your whole body as one from facing West to facing North . Lower your left toes again. True to the name, your arms here are formed as if they are sloping mountainsides. Both of your arms are again drawn, first downward, in an arc toward your right side.