Figure 24. Variation in clast lithology and size ratio of sandstone and quartzite clasts for sites along the study area, Chetco River, Oregon. (A) Variation in clast lithology for each of the 18 surface-material samples taken from 12 bars along the mainstem Chetco River and 3 tributary bars. Sample locations are listed in table 4, but locations proceed downstream in order of sample identifier. Quartzite, sandstone, and a blend of upper-drainage-basin specific lithologies (including coarse-grained igneous, metamorphic, and ultramafic rocks) were the dominant lithologies at the mainstem Chetco River sampling sites. Samples 1b and 1a were done with slightly different protocol, so results not directly comparable. Totals do not sum to 100 percent because unidentified and minor local clast types are not included. (B) Median diameter (d₅₀) of sandstone and quartzite particles at each of the mainstem Chetco sites where surface material was sampled, and downstream trend in the ratios of median diameters. The ratios of sandstone to quartzite d₅₀ at each site indicate a general downstream trend of decreasing sandstone size relative to quartzite size.

Revised July 2012

First posted May 26, 2010