Since the diameter of De Moraes crater (orange words near base in photo) is about 45-46 km across, we can assume since the alien structure covers 1/3 of that crater, then the alien base is 15-15.3 km across or 9.32 miles or 564.1 yards across.

I was looking over some moon maps as many of you know I like to do and I came across an unusual building near De Moraes crater. This crater is located on the northern part of the moon's far side. This object looks like a moon base of some sorts and has definite shapes that tell us it was designed by aliens. Most likely this object could also move from place to place, landing where convenient. I took three screenshots on my Galaxy Note and the moon map program is downloadable for free called "Moon Maps."

It is a 2D atlas that uses Clementine mission photos and Lunar Orbiter mission photos.