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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />001142 <br /> <br />with lateral thick.ening and thinning. The thick.ness of the sandstone beds <br />controls the development of the prominent bluffs and uneven slopes along the <br />ri ver. <br /> <br />Parachute Creek. Member - Green River Formation (Tgp) and Uinta Formation (Tu) <br />The hi ghest e1 evati ons in the lower study area to the south and southwest of <br />the river are fonned by marl stone c1 iffs of the Parachute Creek. Member of the <br />Green Ri ver Fonnati on. The oi 1 ri ch marl stone uni tis about 1,000 feet <br />thick.. The cliffs are capped by weak. sandstones and marl stones of the Uinta <br />Fonnation. Weathering of this unit has produced the gently rolling topography <br />of the Pi ceance Creek. Basi n whi ch supports sparse vegetati on, primari 1y of <br />scrub oak.. <br /> <br />Basalt Flows (Tbb) and Browns Park Formation (Tbp) <br />The youngest bedrock. uni ts in the study area are basal t flows and contempor- <br />aneous sandstone, siltstone, and ash deposits of the Browns Park. Formation. <br />These units are of Tertiary age and are found in the upper White River Basin. <br />They uncomfonnab1y overlie the older sedimentary units and. their near- <br />horizontal dip results in the "Flat Tops" of the highest mountains in the <br />White River National Forest. <br /> <br />4.2 Quaternary Geology <br /> <br />Quaternary deposits are generally confined to lower elevations along the <br />course of the White River. With the exception of the older stream terraces <br />and alluvial fans, these deposits are still accumulating. Units are generally <br />unconso1 i dated and crudely stratifi ed. Thi ck.ness and morphology range wi dely <br />between different units and are dependent upon the rate of outcrop weathering, <br />mechanism of sediment transport, and transport distance. <br /> <br />Terrace Deposits (Qt) <br />The oldest Quaternary units are the terrace gravels, which are distinguished <br />by nearly horizontal, even surfaces. Although younger terraces occurring at <br />lower elevations are more extensive, remnants of older terraces are found at <br />elevations as high as 280 feet above the present level of <br /> <br />4-5 <br />