SAND MOUNTAIN VOLCANIC FIELD UPDATE: COMPLETION OF A FIVE DECADE MAPPING PROJECT IN THE HIGH CASCADE RANGE OF OREGON

The Sand Mountain volcanic field is a ca. 3 ka High Cascade basaltic and basaltic andesite lava field covering 76 km² in central Oregon. The Sand Mountain lavas are known for their burial and blockage of the upper McKenzie River drainage, resulting in the creation of several large freshwater springs and a drowned forest in Clear Lake. Sahalie and Koosah Falls in the upper McKenzie valley result from flowing over Sand Mountain lava. Despite the fields’ young age, mapping individual flows or eruptive events has been difficult due to forest cover, the complexity of the eruptive history, and the difficulty of distinguishing many olivine-phyric only flows in the field. The first detailed mapping of the field by Taylor (1965), using aerial photography, was later improved with major element geochemistry to produce the version shown on the Bend 1:100,000 sheet (Sherrod et al., 2004). More recent mapping by the first two authors using LiDAR coverage of the southern end of the field and extensive major and trace element geochemistry resulted in modification of Taylor’s map and the recognition of 15 eruptive units (Deligne, et al., 2016). Full LiDAR coverage of the field became available in 2016. The LiDAR imagery, along with additional major and trace element geochemistry, has allowed completion of this decades-long effort to map and better understand this complex Holocene lava field. The Sand Mountain field illustrates some difficulties using LiDAR imagery on its own, for example contacts of different units of similar thickness banked against each other are invisible to LiDAR, as are very thin flow margins.

Deligne, N.I., and others, 2016, GSAB, v. 128, p. 1618–1635

Sherrod, D.R., and others, 2004, USGS Map I–2683.

Taylor, E.M., 1965, Ore Bin, v. 27, p. 121–147.