Studies of Yucca Mountain, Nevada, as a potential geologic nuclear-waste repository began in the late 1970s and continued to 1988 when the U. S. Nuclear Regulatory Commission determined that the quality assurance (QA) programs in place were not adequate and demanded restructuring to a new QA program. The new QA program was accepted in 1989, but many activities did not resume until new procedures were in place, until the early 1990s. These two generations of QA programs have resulted in a highly convoluted assignment of qualified (Q)-status for much of the data related to boreholes. In the simplest case, any data that came from boreholes drilled before 1989 had been assigned non-qualified (non-Q) status, and all post1989 boreholes (none of which were drilled until 1991) have been assigned Q status. This pre- and post1989 distinction in Q status of borehole data has meant that lithostratigraphic descriptions and contacts from the pre-1989 boreholes have been classed as non-Q, and any models' that used these data also carried the non-Q status (R.W. Clayton, W.P. Zelinski, and C.A. Rautman, TRW Environmental Safety Systems, Inc., written commun., 1997). This Q-status barrier has also limited the amount of lithostratigraphic work done on the pre-1989 boreholes because of the drive to produce Q-status descriptive reports that contain only Q-status data. A parallel and critical concern that arises from such a long history of data collection is the consistent identification of lithostratigraphic units. In the spring of 1996, an intensive effort began to reexamine 11 lithostratigraphic contacts in boreholes. This work was expanded in 1997 to include as many as 50 lithostratigraphic contacts in 80 boreholes. All this work has been done under the post-1989 QA program and emphasizes technically consistent contacts and the Q-status of each contact rather than carteblanche assignment by borehole.