Rives Salient was located approximately where the new Confederate line joined the old Dimmock Line, and is the location given by Chamberlain himself in several postwar accounts.  (See, for example, pp. 26--27 of the 1974 Morningside Press edition of Chamberlain's memoir, The Passing of the Armies)  However, given that Chamberlain was in a hospital for a full two months after being shot, his personal account of where he was may not be the most accurate.  There is reason to believe that Chamberlain's attack was actually directed further north, near to where the mine would eventually be dug.  An extensive discussion of this issue may be found among the comments to this blog entry

Brig. Gen. Joshua L. Chamberlain