7818 LARIMER RD B Geotech Report 2022-10-25

LEGEND Qoal OLDER ALLUVIUM (HOLOCENE) - This unit includes deposits of mostly clean, stratified, gray to oxidised (to shades of brown) sand and gravel, with some sandy, pebbly, organic -rich silt. It includes colluvium along the bases of adjacent steep slopes. Clasts are varied in composition and are similar to those in the recessional outwash. The older alluvium is 1 to 5 m thick. It partly is a terrace landform several meters above the adjacent flood plain underlain by the younger alluvium. The older alluvium is partly covered by a series of young alluvial fans deposited by the numerous small streams flowing from the steep valley slope out onto the flood plain. The older alluvium is mostly well drained. It lies unconformably on the older underlying deposits Qtb TRANSITIONAL BEDS (FRASER GLACIATION TO PRE-7RASER GLACIATION) - These deposits consist of clay, silt, and very fine to fine sand; some layers of peaty sand and gravel are in the lower part of compact but may be unstable because of high moisture content, plasticity, and local vertical jointing. The sediments were mostly deposited in still to slowly moving water, except for the coarse stream deposits in the lower part of the unit. The unit Includes the Pilchuck Clay Member of the Vashon Drift (Newcomb, 1952), the Admiralty Clay, and pan of the Whidbey Formation (Smith, 1976), particularly near the west edge of the quadrangle. The term "transitional beds" is an informal name originally used by the author In the Mukilteo quadrangle (Minard,1982a) Qva ADVANCE OUTWASH - These deposits underlie the till. They consist of clean, mostly gray, well stratified, unconsolidated sand with pebbles and some cobbles. It is locally silty and oxidized to shades of brown. Clasts are varied in composition and are similar to thosc in the rcccssional outwash. The advance outwash is as much as 70 m thick in outcrop in the quadrangle. It was deposited as bar and channel sediment in and along meltwater streams flowing from the advancing Vashon glacier, and as deltas in ponded areas. The advance outwash is one of the thickest and most ex-ensive aquifers in the region. It lies conformably on the transitional beds. As mapped, the advance outwash contains the Esperance Sand Member of the Vashon Drift (Newcomb, 1952) (equivalent to Esperance sand as used by Smith, 1976) and the Upper Esperance coarse advance outwash (as designated by Smith, 1976) T REFERENCE U.S. GEOLOGIC SURVEY AM41127. N GF.osr.Rv�cr_s nC,4.2'6.��2 � � FIGURE 3: GEOLOGIC MAP nmcncvngr.»crvicccuom