This section advances the theory that many of the odd shaped hills on Mars are hollow, and were possibly either constructed or hollowed out by the inhabitants. To support this theory there are many photos of hills in the process of collapsing, and some that have virtually disappeared but for the original outline. Hills are normally made out of solid rock or earth, yet these hills are full of caves to the point where a collapse makes them virtually disappear. There does not seem to be a geological explanation for the formation of hollow hills. These dwellings appear to be somewhat nonlinear, though survey marks show angles in multiples of 5.

This from photo 40505 has the same outline as the other hills, yet has collapsed. Note the middle ridge which would have supported the structure.   This is just beneath the previous structure and shows a partial collapse of the roof.

Another partial collapse with the same ridge through the center.   Other partial collapses . here .  here .

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