Over the last 20 years, knowledge of the stratigraphy and ages of rock units in the John Day Basin has improved dramatically.
Multiple researchers have worked in all three units of the monument and surrounding areas to produce a detailed stratigraphic framework for this region. (2008) refined the stratigraphy of the Mascall Formation, while work continues on revision of the stratigraphy of the Rattlesnake Formation begun by Martin and Fremd (2001).
In contrast to many records of human history, however, layers of the "fossil record" come without universally recognized methods of dating.
Contract work done by Greg Retallack and Eric Bestland provided a stratigraphic framework for the Clarno and Painted Hills units of the monument, primarily rocks from the Clarno and John Day Formations (Bestland and Retallack 1994a, b, Bestland et al. Hunt and Stepleton (2004) completely redefined the upper part of the John Day Formation, splitting the "Haystack Valley Member" into a series of four distinct members. (2008) expanded on these studies to produce a revised composite stratigraphy of the entire complex sequence of beds from the John Day Formation, including 7 members and more than 20 lithostratigraphic units (Fremd et al. Radiometric dates from a number of sources have been combined with lithostratigraphic and magnetostratigraphic data to produce a highly refined chronostratigraphy of rock layers exposed throughout the region.
Many dates were part of the doctoral dissertation of Carl C.
The fossil record is a "recording" of history made out of layers of fossils.
Much like the growth rings in a tree or the layers found in ice cores, the earth is covered in layers (strata) of sedimentary rock which represent a sequence of events.
As a result, there is a changing ratio of carbon-14 to the more atomically stable carbon-12 involves actually counting individual carbon-14 atoms.