since Reck's time have utilized Reck's original Bed outline, adding clarity, detail, and corrections to achieve a more thorough understanding of gorge history. Reck's original Bed IV interval was later distinguished as consisting of Bed IV and the Masek Beds, while Bed V has been reclassified as the Ndutu Bed and the Naisiuiu Bed. Gorge Stratigraphy The stratigraphic sequence in the gorge is up to 90 m thick, with a welded tuff, the Naabi ignimbrite, forming the base. This is overlain by a series of lava flows from Olmoti and from another source to the south. The oldest fossils are found on this surface, dated at 1.89 mya, while stone tools have been dated at 1.7 mya through the first use of K-Ar dating by Garniss Curtis. In addition, fission track dating and paleomagnetism were used to date the deposits, while amino acid dating and Carbon-14 dating were used to date the bones. Hominid fossils and stone tools are found continuously throughout the entire exposed sequence in the gorge. Faulting between 100 and 30 kya, formed the Olbalbal Depression northwest of Ngorongoro. Bed I The 20–46 m thick Lower Pleistocene Bed I sediments overlying the Naabi ignimbrite consist of layers of Olmoti tuff and lake sediment claystone. Four well-preserved living sites of note are located within Bed I, the FLK and FLK North-North sites mentioned above, plus DK and FLK North. The DK site (Donald McInnes' first initial plus k for korongo) has what Leakey considers to be a stone circle, and also many tools and fossil bones ranging in age from 1.75 mya to 1.9 mya. Bed II Bed II consists of 21–35 m of clay and sandstone Olduvai Lake and stream deposits. Manuports are abundant at the MNK (Mark Nicol Korongo) site in addition to a chert nodule quarry containing over 14,000 pieces, including gneiss and lava anvils and hammerstones. Hand axes were found at the EF-HR (Evelyn Fuchs-Hans Reck) and TK (Thiongo Korongo) sites. The BK (Bell's Korongo) site contained an Australopithecus boisei deciduous molar and canine. Bed III The distinctly red Bed III consists of 6–10 m of clays, sandstones and conglomerates signifying variable lake depths. Few fossils are present and only isolated stone tools, indicating a sparse early man presence. Bed IV Bed IV is a distinctly different unit from Bed II in the eastern portion of the gorge. There, it is 5–8 m thick