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Show En route from Stop [ 4] to Stop [ 5]. If time permits, we will make a brief stop near the open gate to examine an algal bioherm ( tufa reef, stromatolite mass, or whatever). The purposes of this optional stop are to examine some of these features, discuss some of their salient properties- including apparent age and biological contents- and speculate on possible origins and potential implications, if any. Apparently restricted to within a radius of about 10 kilometers near the hydro- isostatic centroid, and to within + 5 m of present lake level within that radius, there are about a dozen rather large bioherms or swarms of small bioherms/ stromatolites. In the last few years, several groups of researchers have begun to study at least two of the larger bioherms. Stop [ 5], ( Hovingh on the Skull Valley subbasin and Horseshoe Springs, including the influence of paleolakes on the distribution of aquatic fauna) In the Bonneville basin, the gastropod Tryonia is found near Grantsville, in the Horseshoe Springs area, at Fish Springs, at Blue Lake, and as fossils associated with an extinct spring near Wendover ( near the Pleistocene- Holocene boundary in Jukebox Trench, where they have a ground- water skewed radiocarbon age that is too old by a factor of two); a feature that is common to all these springs is close proximity to the Gilbert shoreline. The leech Erpobdella dubia is found in springs above the Bonneville shoreline, and not in springs at levels inundated by Lake Bonneville; this suggests that lake history prevented the leech from entering springs at lower elevations within the basin. En route from Stop [ 5] to Stop [ 6]. On the W side of the Skull Valley highway, about 20 km S of Horseshoe Springs, the Goshute Tribe and a consortium of public utilities are proposing to build a large nuclear waste storage facility. Needless to say, this is generating quite a flap. Stop [ 6], ( Madsen on the Devils Gate Neotoma middens) The Devils Gate middens are part of a series of more than 60 dated Bonneville basin plant macrofossil records derived from fossil woodrat { Neotoma spp.) nests. The majority of these middens ( including several of the Devils Gate middens) date to the Pleistocene/ Holocene transition. Together, they suggest that cold montane steppe, dominated by sagebrush, snowberry, and current, covered much of the western Bonneville basin prior to 13 ka. From - 13 ka to shortly after 11 ka the region was vegetated by limber pine ( Pinus flexilis) woodland in lower montane settings, and by a mosaic of limber pine and sagebrush steppe along basin- floor margins. This mosaic was replaced by more xeric desert shrub dominated by sagebrush { Artemisia tridentata) and shadscale { Atriplex confertifolia), with rocky mountain juniper { Juniperus scopulorum) on lower montane areas. The growth of limber pine at elevations below 4400 ft suggests that summer temperatures were as much as 6° C cooler than at present during the 13- 11 ka period. The early Holocene ( 10- 8 ka) was probably 2- 3° C cooler than now. En route from Stop [ 6] to Stop [ 7]. ( Hovingh on aquatic fauna isolates in the Rush Valley subbasin) No aquatic- dependent amphibian ( Ranidae, Bufonidae, Hylidae) has been found in Rush Valley. The leech Nephelopsis obscura has been found below the Bonneville shoreline and the leech Erpobdella dubia has been found above the highest |
