Coquille Subbasin Working Atlas - p7
Geology
Page 6: Vegetation and Land Cover
Page 7: Geology
Page 8: Water Use and Availability
Page 9: Fish Distribution & Habitat
The general geologic units present within the Coquille subbasin are shown in the Geology map, based on the 1:500,000 scale State Geology Map (Walker and McLeod, 1991). The legend shown on the Geology map is an abbreviated version of the map legend compiled by the Oregon Department of Geology, providing detailed descriptions of the characteristics of the units. Other geologic data of the Coquille Basin can be found in several publications (Ricks, 1992, State Water Resources Board, 1963, Power Rangers District Siskiyou National Forest, 1994, Hurtado et al., 1992). The interpretive legend provided in Table 12 was developed specifically for this atlas by the Oregon Department of Geology to provide greater understanding of the relative stability and erodability of the major geologic types within the subbasin.
The Coquille subbasin is dominated by marine sedimentary rocks. The two major geologic features of the Coquille are the southern part of the Coast Range and the northwestern corner of the Klamath Mountains. The headwaters of the South Fork of the Coquille River lie in the Klamath Mountains, which is a hard rock system composed of volcanics, diorite, and serpentine rocks. Fault contacts exist between several of the volcanic rocks leading to instability in the area resulting in earthflows and debris slides and slumps (State Water Resources, 1963, Ricks, 1992). Other forks in the basin are in the Coast Range and are primarily steeply sloped sandstone (Nonpoint Source Effort, 1992). A major formation present within the Coast Range area of the basin is the Tyee, which is composed of a thick sequence of bedded sandstone, susceptible to mass movement, rapid erosion, flash flooding, and landslides.
[click on map for larger version]
| Table 12: Interpretive Geology Legend | |
| Qt | 21,647 acres. Marine terrace and gravels. Gentle slopes. Unconsolidated deposits of gravel, cobbles and boulders intermixed with mud and sand. Erodes to sand and mud. Hazards include headland erosion, stream-bank erosion, and ponding. Groundwater potential is low to moderate. |
| Qls | 2,803 acres. Landslide and debris-flow deposits. Mixture of rock fragments and unstratified soils. Erodes to mud and sand. Forms gentle to moderate slopes. Variable rock and engineering conditions with extreme behavioral variation in artificial cuts. |
| Js | 14,743 acres. Sedimentary rock. Mudstone, shale, siltstone, tuff limestone and metamorphic rock. Moderate slope, irregular drainage, irregular soil distribution, and irregular topography. Susceptible to landslides (earthflows). |
| Qal | 22.445 acres. Muds, sands and gravels. Easily eroded by streams. Gentle slopes form. Soil rich in organic material. Hazards include flooding, and rapid erosion and deposition within the flood plain and streams. High groundwater potential. |
| Qd | 1,303 acres. Dune and beach sand. Unconsolidated fine to medium grained sands. Susceptible to stream and wind erosion except in areas of high vegetative cover. Rapid deposition occurs along coast line. Good groundwater potential. |
| Tmsm | 128,023 acres. Alternating beds of sandstone and mudstone with rock material present. Erodes to sand and mud. Rapid erosion and deposition along flood plain, slopes, and stream banks. Gentle to moderate slope. Very susceptible to landslides (earthflows) on steep slopes. Low groundwater potential. |
| KJds | 48,733 acres. Sedimentary rock. Sandstone interbedded with a mixture of sand, mud, and rock. Susceptible to slope erosion, stream bank erosion and landslides (mass movement and earthflows). Moderate slope, irregular drainage, irregular soil distribution, and irregular topography. Slumping most common south of Coquille River. |
| Tmsc | 88,086 acres. Marine sandstone, and mudstone (alternating beds). Sedimentary. Erosion occurs particularly in flood plain. Gentle to moderate slopes form less hazards. Cobble and pebble conglomerates. |
| Ju | 6,045 acres. Iron and magnesium rich rock formed at depth. Moderate slope. Very susceptible to landslides (earthflow and slump). |
| Tt | 200,694 acres. Thick sequence of rhythmically bedded sandstone with thinly bedded mudstone. Low porosity of water infiltration except along joints. Susceptible to rapid erosion, flash flooding, stream bank erosion, and rapid landslides (mass movement, debris flow, and rock slides). Moderate to steep slopes occur. High debris flow potential on steep slopes. Low groundwater potential. Constrained channels. Weathers to sandy silt. |
| Tmss | 59,080 acres. Fine to coarse grained sandstone held together by solidified muds. Easily eroded, weathers to a gentle slope consisting of fine to coarse grained muds and sands. Susceptible to landslides and being easily cut by river channels. |
| Jv | 622 acres. Volcanic rocks. Stable cliff forming rock. Weathers to steep slopes and commonly forms canyon walls. Erodes to mud and capable of filling streams and rivers with suspended muddy material. |
| KJm | 6,001 acres. Sandstone and conglomerate; rocks are rich in calcium carbonate. Easily eroded. Weathers to muds, sands, and rock fragments. Gentle to medium slope forms. Low groundwater potential. |
| Tss | 48,141 acres. Alternating beds of mudstone and sandstone varying in thickness; fine to coarse grained. Erodes to mud and sand. Weathers to gentle slope. Susceptible to rapid erosion on slopes and stream banks. Landslides (earthflows and slumping) are common south of the Coquille River. Minimal groundwater. |
| Tsr | 11,525 acres. Volcanic material; basalt. Gentle to moderate slopes form. Landslides (slumping and earthflows) occur in steeply sloping areas. Very low groundwater potential. |
| Ks | 205 acres. Sedimentary rocks (Cretaceous). |
| OW | 918 acres. Other undefined. |
