In evaluating boundaries I have relied most heavily on the information of Merriam (map 3) and Kroeber (map 1). Merriam's data are contained in a 1:500,000 map of California, together with a descriptive text. The map and the description were made up by Dr. Merriam's daughter, Mrs. Zenaida Merriam Talbot, during the years 1939 to 1946, from information in Merriam's notes and journals, the latter of which are not accessible to this writer. Often, where Merriam's boundaries disagree with those of Kroeber or other authors, Merriam's line will follow a stream, whereas the alternative follows a ridge or drainage diversion. When the evidence is inconclusive, I have usually followed Kroeber's method and chosen the ridge rather than the stream as the boundary. In this area the streams are small and easily crossed during most of the year and therefore would not constitute a barrier sufficient for the divergence of dialects. On the other hand, the hills were visited only briefly for hunting and gathering; the population depended to a great extent on the products of streams for its subsistence, and consequently all the permanent villages were in the lowlands and canyons. For this reason, the ridges rather than the streams would tend to be boundaries. Kroeber has discussed this point more generally (1939, p. 216) and also in greater detail (1925_a_, p. 160).
The southern boundary of the Athabascans begins at Usal Creek on the coast and goes eastward for a few miles before swinging south to include the drainages of Hollow Tree Creek and the South Fork of the Eel in Kato territory. It turns north to enclose the headwaters of South Fork and proceeds along the ridge dividing Ten Mile Creek from the main Eel until it reaches the drainage of Blue Rock Creek; it then passes around north of the creek and crosses the Eel near the mouth of the creek. From this point it runs in an easterly direction around the drainage of Hulls Creek.
Kroeber's map in the Handbook shows the southern boundary beginning a few miles south of Usal Creek, but Merriam and Nomland both maintain that the creek itself is the boundary and Gifford (1939, p. 304) says that both Sinkyone and Yuki were spoken in the village situated at the mouth of the creek. The information of all four authors came from either Sally or Tom Bell, wife and husband, who are respectively Shelter Cove Sinkyone and Coast Yuki. I have accepted Merriam's boundary, since it agrees with Nomland's.