The images above show the "Stright Wall", a lunar fault line that has shifted to form a 60 mile long, 800 foot high cliff.
The fault line is near the center of the moon's face. The first image shows it at first quarter, when sunlight is shining from the right, which is the higher side of the cliff, so the cliff casts a shadow which forms a straight black line. The second (2X close-up) image was taken at third quarter, so the sunlight is shining at the face of the cliff.
CCD images at prime focus (first image), and with a 2X barlow (second image).
