Carol Hill and Victor Polyak passed along news that their paper on karst hydrology of the Grand Canyon has been published. They conclude that "The karst hydrology of Grand Canyon may be unique compared to other hypogene cave areas of the world." [right, Figure 13 from the paper: "Gypsum rind in an eastern Grand Canyon cave. This is not a speleothemic gypsum crust but a speleogenetic gypsum rind that formed just above the water table as a replacement of the limestone bedrock." Photo by Bob Buecher]
"Descent of the potentiometric surface (or water table) over time is recorded by one ore episode and six cave episodes: (1) emplacement of Cu–U ore, (2) precipitation of iron oxide in cavities, (3) dissolution of cave passages, (4) precipitation of calcite-spar linings over cave passage walls, (5) precipitation of cave mammillary coatings, (6) minor replacement of cave wall and ceiling limestone by gypsum, and (7) deposition of subaerial speleothems."
Ref: "Karst Hydrology of Grand Canyon, Arizona, USA," C.A. Hill, & V.J. Polyak, Sept. 2010, Journal of Hydrology, v. 390, p. 169-181.