Around
30,000 years ago the field direction at Mono Lake took two
sizeable swings away from the usual direction, as shown
in this plot by the two loops made by the virtual geomagnetic
pole away from the north pole. The excursion lasted about
2,000 years, and the field intensity appears to have dropped
lower and then grown higher than that immediately before
and after the excursion. It has been identified unambiguously
in other basins in Nevada and Oregon, and possibly in records
more distant, but it is still an open question whether the
Mono Lake Excursion was worldwide or only regional in extent.
