REVISED MAPPING OF THE LOCATION AND EXTENT OF GLACIATION IN THE CENTRAL OREGON CASCADES BASED ON LIDAR DATA

The glacial chronology of the central Oregon Cascades was initially described by Scott in the Metolius River basin (1977), then revised and expanded by Bevis to include the McKenzie River drainage (2008), the Whychus Creek drainage (2011a and 2011b) and the Deschutes River basin (2013). This updated chronology consists of two major periods of glaciation: 1) the Cabot Creek, correlated with oxygen-isotope stage 2 and the late Pleistocene Last Glacial Maximum (LGM); and 2) the Jack Creek, correlated with oxygen-isotope stage 6 and late middle Pleistocene glaciation. Scott and Bevis also recognized two advances during the Cabot Creek glaciation, the older Suttle Lake corresponding to the LGM, and the younger Canyon Creek corresponding to at least two minor readvances or stillstands at the close of the late Pleistocene. Although neoglacial activity was not included in the work of Bevis, Scott identified two phases of Late Holocene neoglaciation he named the Jefferson Park advances. The basis for the Scott-Bevis chronology was field mapping aided by aerial photos and topographic maps, and the use of relative dating techniques. Significantly, this chronology was developed prior to the advent of LiDAR coverage for the central Oregon Cascades. Our present investigation utilized available LiDAR data to remap the glacial deposits over much of the region covered by Scott and Bevis from LiDAR-based, shaded-relief maps we devised using 3D Analyst in ArcGIS 10.5. We compared previously mapped moraines and the extent of glacial deposits from topographic maps, to shaded-relief maps based on standard 10-meter resolution DEM data, and to our LiDAR maps (with a resolution of 1-2 meters). We recognized numerous moraines that were not previously mapped. While the master glacial chronology was ultimately unaffected by our work, much detail was added to the subtleties of field mapping. The maximum extent of the Jack Creek glaciation was revised in several locations, and revision of the Cabot Creek glaciation included recognition of unmapped Suttle Lake end moraines, but especially the recognition of recessional Canyon Creek moraines in many locations. We also added considerable detail to the location and extent of Jefferson Park moraines, distinguishing two sets of moraines of probable Little Ice Age origin throughout the region.