- Geologic Map of the East Half of the Bellevue South 7.5’ x 15’ Quadrangle, Issaquah Area, King County, Washington
The Issaquah area includes several of the most outstanding geologic features of the eastern Puget Lowland region. Folds have warped thousands of meters of Tertiary sedimentary and volcanic rocks. Several hundred meters of both glacial and postglacial sediment have accumulated in a deep glacial trough, which is now partly occupied by Lake Sammamish but which was previously the conduit for massive volumes of meltwater during ice-sheet occupation and retreat. The eastern projection of an east-west-oriented crustal structure, which reflects Tertiary through Holocene fault displacement, extends across the eastern part of the map area.
- Tukwila Formation—Andesitic to dacitic volcanic sandstone, siltstone, shale, tuff-breccia, tuff, volcanic mudflow (lahar), carbonaceous shales, and minor lava flows or sills. Typically massive; only local sedimentary interbeds indicate structure. K-Ar age on plagioclase from tuff-breccia at top of unit, about 3 km west of quadrangle, yielded an age of 42.0±2.4 Ma (Turner and others, 1983)
- Denny Camp Falls (waterfallsnorthwest.com)
Denny Camp Falls is likely the largest of a number of small waterfalls found both above and below Franklin Falls along the South Fork Snoqualmie River. Conveniently this waterfall happens to be situated almost immediately to a road and features quite easy access (though clear views require a bit of less-than-easy scrambling). The river here constricts between narrow gorge walls and plunges 27 feet into a small bowl flanked by dark mossy cliffs. Because of the constricted gorge walls, the Franklin Falls trail which passes the falls has to divert almost quite literally onto Denny Creek Road #58, and this fortunately facilitates quick in-and-out access for those looking to visit several waterfalls in the area in one day.
- Tukwila Formation (en.wikipedia.og)
The Tukwila Formation is a geological formation in King County, Washington within the Puget Group. It is named after Tukwila area, which is close to the formation. The formation consists of various fossils of marine origin.