Nice picture Marcia, I'd love to see the stereo pair of this one!
Looks to me not like a "coast", but rather the outcrop pattern of the "white unit" (Opportunity Formation). Since the unit is flat, it will create an outcrop pattern that mimics the contour lines.
I recall the comments from Nick's reporting and that of the guy I rode the ski lift with indicating that the white unit was "hundreds of meters thick" and could be seen "outcropping at the edges of the plain."