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In addition, one of the following statements should be included. Abstract The Piceance Basin, CO is a type locale for unconventional tight-gas sandstone in the Rocky Mountains (Law, 2002). Productive Williams Fork sandstones are extremely heterogeneous fluvial to marginal marine reservoirs that have very low permeability (<0.1 md) that typically require expensive hydraulic fracturing with 10-20 acre well spacing to produce. Despite the enormous gas potential of the Piceance Basin many wells can be uneconomic unless higher permeability fairways are found. Although many new completion and stimulation technologies have vastly improved production, higher-than-average permeability zones that result from improved matrix porosity and/or natural fracture systems are needed to ensure economic wells. Geologic controls on higher-than-average permeability zones are complex and poorly understood; these controls include controls on reservoir quality, fracture development and compartmentalization such as depositional environment, diagenesis, mechanical rock properties and strain. This study presents a regional sequence-stratigraphic framework that integrates outcrop and subsurface data to better understand the stratigraphic controls on tight-gas sand production. Improved understanding of the regional stratigraphic framework provides the foundation for predicting " sweet spots " in tight-gas sandstone reservoirs. The integration of 17 stratigraphic profiles, detailed facies analysis, detrital composition, paleocurrent data, synthetic GR curves from hand-held spectrometer and 104 well logs delineated key stratigraphic stacking patterns and sequence-stratigraphic surfaces that were correlated into the subsurface at a basin-scale. Thirty-four facies defined five main cycles within the predominantly fluvial to paludal lower Williams Fork Formation: (1) Cycle A-Tidal/coastal plain to single-story meandering fluvial, (2) Cycle B-Tidal/coastal plain to vertically-stacked meandering fluvial with floodplain, (3) Cycle C-single-story, meandering fluvial with undifferentiated floodplain to vertically-stacked meandering fluvial, (4) Cycle D-Tidal/coastal plain to anastomosed fluvial complex, and (5) Cycle E-Anastomosed fluvial complex to single-story, meandering fluvial with undifferentiated floodplain. Based on radiometrically constrained ammonite data, the total time duration of the study interval is estimated at 1.5 My (75.08 Ma to 73.52 Ma). Six complete, high-frequency (4 th order) depositional sequences were identified with an estimated duration of 260 ky each in the lower Williams Fork and Rollins Sandstone. The higher-frequencey sequences build into two sequence sets. An older, retrogradational to aggradational (i.e., transgressive) sequence set A consists of iv more poorly connected anastomosed fluvial, tidal-fluvial and paludal sandstones, whereas the younger progradational to aggradational (i.e., highstand to lowstand) sequence set B consists of cycles of better connected, sandier meandering fluvial anastomosed. Isopach maps of sequence …