A Grass Valley man died in a motorcycle accident Wednesday morning on westbound Interstate 84 just west of Mosier.  According to the Oregon State Police, a preliminary investigation revealed 60-year-old Mike Layton Wallace was traveling westbound in the slow lane at or just below the speed limit.  A witness who was following Wallace observed him reaching back towards a saddle bag along the left rear side of the motorcycle when he lost control and began to wobble back and forth.  Wallace was ejected off the motorcycle and came to rest along the shoulder.  The motorcycle traveled under its own power before stopping along the center median about 1,000 feet from Wallace.  Officers and medical personnel arriving at the scene determined Wallace had succumbed to injuries sustained in the accident.