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_r: .~ .J , .~ ~ j t t ", . }::;.:fi;2~2~'~\'~->? ':~;:< _ +_ . .. ~ ~ .; . C.F. WaYlhomas. R.D. Jarr~tt/Geomorphology II (/994) ls-+o 21 Fig.":'. ill.) FB2 boulder bar. site 1. View is downscremn (northeast) toward inlet to Horserooth Reservoir. (b) FBllongitudinlll boulder bar (;liTO......) on right bank.. site 4. View is toward the south. (e) IrnbriClted flood boulders ne:lrthe mouth of Anhurs Rock c:tnyon. 4.i. Relative-age criteria R,!ative.age data collected at each site includes micro-pitting, grain relief, lichen cover, boulder burial. and surface boulder weathering (Table 2). Data were collected from 25-50 boulders in each deposit. Micro- pits ar. surface depressions that are and typically less than 0.5 cm deep. Su~ features are common if present on more than 75% of the boulder surf,ce. rare if present on less than 10% of the boulder suriace. and incipient if the pits are small but aerially abundant. Grain relief is the amount of surface relief produced by weathering of mineral grains. We esti- mated the percentage of quartz and feldspar grains in relief on individual flood boulders and examined 25- 50 boulders per deposit. Data are reported as an esti- mate for the entire deposit (Table 2). Lichen cover is the estimated percentage of lichen growing on each flood boulder. Data are reported as an average based on examination of 25-50 boulders. Boulder burial refers to the percentage of the total boulder surface exposed above ground. Boulder buriill is related to the addition of new sediment at the site (colluvium, eolian, slope wash). boulder size reduction by weathering. and the original relief across the surface of the flood deposit. If).zenera!, the amount of boulder burial increases with time. Data are reported as an estimate for the entire deposit. Surface boulder weathering is the proportion of fresh, partially weathered and weathered granodior- ite boulders in a flood deposit. Fresh boulders are those that exhibit less than 5% minera! grains in relief. Weathered boulders are those that exhibit more than 90% mineral grains in relief and show abundant surface pitting and spalling. Partially-weathered boulders are those that possess characteristics intermediate between weathered and, fresh boulders. The weathering of flood boulders and lichen colo- nization of boulder surfaces is complicated by the ' effects of forest and range fires that likely happened in the region during the1ate Quaternary (Birkeland, 1984, pp. 63-65). 'Fire is an important factor in rock weath- . ering because thenna! expansion of the rOck may cause complete or partial spalling of the boulder surface (Blackwelder. 1927; Bierman and Gillespie, 1991). If the outer part of the boulder spalls after a lire the boul~ der weathering "clock" is essentially reset and the