Oriented samples collected for
paleomagnetic analysis from sediments of the
newly-named Mojave River Formation (Nagy
& Murray, 1991, this volume) possess stable
characteristic components of Natural
Remanent Magnetization (NRM). Progressive
demagnetization reveals characteristic
components of both normal and reversed
polarity which are stratigraphically distinct.
The oldest sediments exposed within the field
area are reversely magnetized and were
probably deposited during the early portion of
the Matuyama reversed Chron.
Stratigraphically higher units contain what
appears to be the Olduvai normal Subchron,
as well as a shorter normal zone which
probably is either the Cobb Mountain or
Jaramillo Event. The location of the
Brunhes/Matuyama boundary at one site is
within an alluvial fanglomerate which grades
upward conformably into the lowest unit of
the overlying Manix Formation, possibly
accounting for the absence of the Bishop ash
in the section.
Demagnetization data from 143 samples
yielding acceptable least-squares lines suggest
a net clockwise rotation of 8 ± 2.7° over the
past two million years, perhaps with some of
the rotation during deposition. This rate of
rotation could account easily for larger
rotations reported elsewhere in the Mojave
Desert on units of Miocene age
