[Ray76]

While harder than the weathered brown rock, the gray rock is not particularly hard.

Moonbeam Canyon was carved in weeks when it should have taken centuries.

[EarthResearcher333]

Hi Ray76, Your own picture demonstrates that a properly emplaced concrete "flip" bucket design remains structurally competent when embedded into hard amphibolite (flip bucket water dispersal blocks with concrete anchored foundation at the end of the main spillway). The structural importance of emplacement in Amphibolite is providing protection from shattering forces similar to impact jackhammering. This is what a competent concrete & rebar structure provides.

However, the erosion debris field reveals how materials became collision shatter instruments from the significant forces of hydraulic turbulence in the blowout flow (canyon). Thus, all of the broken spillway concrete, all of the highly fractured weathered rock, and even ultimately "shattered" pieces of the amphibolite essentially "jackhammered" a "fresh rock erosion" down the canyon.

Throughout all of the geologic reports, the definition of "fresh rock" and "adequate bedrock" applied to the hard amphibolite (and was noted as Amphibolite).