Final answer:
Brian believes the sideways bowl-shaped shelter under a ledge was shaped by natural geologic processes or ancient human activity, suggested by references to unique rock formations, weathering, and erosion.
Step-by-step explanation:
Brian thinks the sideways bowl has formed under a ledge as part of a natural geologic process. The references to folded bedrock, meteor impacts, and erosion hints at a formation through significant geologic timescales. The descriptions of the landscape with its unique rock formations suggest processes such as weathering, erosion, or even ancient human activity for creating such a shelter spot. The excerpts mentioning cylindrical burrows and balancing rocks point towards natural environmental shaping over many years or potential modifications by ancient peoples, for example, the cliff dwellers.