Comments on Geologic Parameters
The only porosity values we found for the Morrison Formation were in an article by Freethey (1987a, p. 63), in which he offered a diagram of effective porosity for the five aquifers (including the Morrison) that he studied in the Colorado Plateau region, exclusive of the San Juan Basin. The mean value for the Morrison is near 13.5 percent, with a standard deviation of approximately 12.5 percent. We took these values directly from the diagram because they were not mentioned in Freethey's (1987a) text. Freethey calculated these values from a total of 22 samples. None of the samples is from our study area, but by extrapolation they provide a general approximation of the porosity in the Morrison of the San Juan Basin.
Freethey, G. W., 1987b, Lithologic and hydrologic properties of Mesozoic rocks in the Upper Colorado River Basin, Mexico, in McLean, J. S., and Johnson, A. I., eds., Regional aquifer systems of the United States-aquifers of the western mountain area: 23rd Annual American Water Resources Association (AWRA) Conference and Symposium, Salt Lake City: AWRA Monograph Series No. 14, p. 81-100.