CHAPTER 11 LTA Descriptions Section M333A-Okanogan Highlands This Section occurs in northeast Washington and northern Idaho and is dominated by Continentally Glaciated Mountains. Nineteen LTAs were mapped in this Section. See Appendix F for a complete list of LTAs and their acreages. Map unit descriptions are preceded by the following illustrations: Figure 45: Map showing location of M333A within the Northern Region Figure 46: M333A landscape photograph Selkirk Mountains, Idaho Panhandle National Forests Figure 47: Map showing distribution of LTAS within M333A Figure 48: Bar chart showing abundance of landform groups within M333A Figure 49: Bar chart showing abundance of geologic material groups within M333A LTA10-M333A VALLEYS: RECENT COARSE ALLUVIUM Location: These units occur in the Selkirk Mountains of the Priest, Pend Oreille, Kootenai and Spokane River basins of northwestern Idaho and northeast Washington. Acreage by Section 10-M333A 38,951 LTA Setting and General Characteristics Differentiating characteristics: This map unit occurs in a valley bottom landscape setting at elevations that range from low to high. The unit is typically composed of wide glacial trough bottoms. Parent materials are surface volcanic ash overlying mostly outwash with a narrow deposit of recent alluvium near the stream. These materials are usually derived from granitic bedrock sources. Accessory Characteristics: The primary soils are generally deep stratified sands. The vegetation is a mosaic of mixed coniferous and alpine forest with associated riparian plants. Mean annual precipitation ranges from 76 to 152 centimeters (30 to 60 inches). The elevation range of this unit is 610 to 1829 meters (2000 to 6000 feet). The dominant slopes have gradients of 2 to 15 percent. LTA Components: This landtype association consists of toeslopes and stream terraces, floodplains, and alluvial basins. Toeslopes and stream terraces are formed in coarse alluvium, some stratified. These toeslopes and terraces have slope gradients that range from 2 to 20 percent. Soils on these landforms are deep, poorly developed and consist mostly of sand and gravel. The major soils are classified as Andic Dystrochrepts and Andic Cryochrepts, along with Typic Udivitrands and Vitric Haplocryands. The dominant potential natural vegetation series on the well drained, high elevation sites are subalpine fir with western hemlock and western redcedar occurring at low to mid-elevations. This component represents about 60 percent of the map unit. Floodplains and alluvial basins are formed in coarse, stratified and unstratified alluvium. These areas have slope gradients that range from 0 to 10 percent. Soils on these landforms are deep, poorly developed and consist mostly of sand and gravel. The major soils are classified as Humic Udivitrands, Vitric Fulvicryands, Pachic Haplumbrepts and Typic Haplaquepts. The dominant potential natural vegetation series are subalpine fir in the higher elevations and cold air drainage areas, with western redcedar in the low and mid-elevations. Compiled by: Jerry Niehoff, Idaho Panhandle National Forests LTA11-M333A VALLEYS: LACUSTRINE SEDIMENTS Location: These units occur in the Selkirk Mountains of the Priest, Pend Oreille, Kootenai and Spokane River basins of northwestern Idaho and northeast Washington. Acreage by Section 11-M333A 220,526 LTA Setting and General Characteristics Differentiating characteristics: This map unit occurs in a valley bottom landscape setting at low elevations. The unit is typically composed of glacial Lacustrine plains, benches and draws. Parent materials are surface volcanic ash overlying silty lake sediments. Accessory Characteristics: The primary soils are deep, silty, lacustrine sediments from unnamed glacial lakes. The vegetation is a mosaic of mixed coniferous forest. Mean annual precipitation ranges from 64 to 76 centimeters (25 to 30 inches). The elevation range of this unit is 536 to 762 meters (1760 to 2500 feet). The dominant slopes have gradients of 0 to 55 percent. LTA Components: This landtype association consists of flat plains, benches and draws. Flat plains, benches and draws are formed in mostly deep fine- silty or coarse-silty lacustrine sediments. Some sandy and loamy sediments also occur. Slope gradients range from 0 to 60 percent. Soils on these landforms are deep, poorly developed and consist mostly of silt with some sands and loams. The deposits found around Bonners Ferry are calcareous. The major soils are classified as Typic Udivitrands. Other soils which occur are Andic Eutrochrepts and Andic Fragixeralfs. The dominant potential natural vegetation series are western redcedar, grand fir, and Douglas-fir. Compiled by: Jerry Niehoff, Idaho Panhandle National Forests LTA12-M333A VALLEYS: OUTWASH AND OTHER OLDER COARSE ALLUVIAL DEPOSITS Location: These units occur in the Selkirk Mountains of the Priest, Pend Oreille, and Spokane River basins of northwestern Idaho and northeast Washington. Acreage by Section 12-M333A 323,513 LTA Setting and General Characteristics Differentiating characteristics: This map unit occurs in a valley bottom landscape setting at elevations that range from low to high. The unit is typically composed outwash plains, alluvial fans and glacial terraces. Parent materials are surface volcanic ash overlying mostly outwash with a narrow deposit of recent alluvium near the stream. These materials are derived from belt and granitic bedrock sources. Accessory Characteristics: The primary soils are deep, intermixed and stratified gravels, sands, and silts. The vegetation is a mosaic of mixed coniferous and alpine forest with associated riparian plants. Mean annual precipitation ranges from 76 to 152 centimeters (30 to 60 inches). The elevation range of this unit is 536 to 1646 meters (1760 to 5400 feet). The dominant slopes have gradients of 0 to 20 percent, but some steep terrace escarpments have gradients up to 75 percent. LTA Components: This landtype association consists of outwash plains, terraces and rolling surfaces. Outwash plains and terraces and rolling surfaces are formed in coarse outwash and alluvium, some stratified. These plains and terraces have slope gradients that generally range from 2 to 20 percent. Soils on these landforms are deep, poorly developed and consist mostly of sand and gravel. The major soils on the well drained sites are classified as Andic Dystrochrepts and Andic Cryochrepts, along with Typic Udivitrands and Vitric Haplocryands. The major soils on the poorly drained sites are classified as Humic Udivitrands, Vitric Fulvicryands, Pachic Haplumbrepts and Typic Haplaquepts. The dominant potential natural vegetation series on the well drained, high elevation sites are subalpine fir, with western hemlock, western redcedar, grand fir and Douglas-fir occurring at low to mid elevations. The dominant potential natural vegetation on the poorly drained sites is subalpine fir in the higher elevations and cold air drainage areas, with western redcedar in the low and mid elevations. Compiled by: Jerry Niehoff, Idaho Panhandle National Forests LTA14-M333A VALLEYS: RECENT FINE ALLUVIUM Location: These units occur in the lower part of the Purcell Trench and the Pend Oreille River basin of northwestern Idaho. Acreage by Section 14-M333A 14,384 LTA Setting and General Characteristics Differentiating Characteristics: This map unit occurs in a valley bottom landscape setting at low elevations. The unit is typically composed low stream terraces, flood plains and bottom lands. Parent materials are surface volcanic ash overlying fine recent alluvium near streams. These materials are derived from belt and granitic bedrock sources. Accessory Characteristics: The primary soils are deep, poorly drained, silt loams and very fine sandy loams. The vegetation is a mosaic of grass meadows with associated riparian plants. Mean annual precipitation ranges from 64 to 76 centimeters (25 to 30 inches). The elevation range is 640 to 914 meters (2100 to 3000 feet). The dominant slopes have gradients of 0 to 4 percent. LTA Components: This landtype association consists of floodplains and bottom lands. Floodplains and bottom lands are formed in fine alluvium. These landscapes have slope gradients that generally range from 0 to 10 percent. Soils on these landforms are very deep and consist mostly of silt loams and very fine sands. The major soils are classified as Mollic Andaquepts, medial, nonacid, frigid; Typic Borosaprists, and Typic Haplaquolls, fine, mixed, frigid. The dominant vegetation consists of grasses, forbs and shrubs. Compiled by: Jerry Niehoff, Idaho Panhandle National Forests Chapter 11 LTA20-M333A BREAKS: METASEDIMENTARY (BELT) Location: These units occur in the St. Joe, Coeur d' Alene and Clearwater Mountains of the Bitterroot range, which are part of the Clark Fork, Coeur d' Alene, St. Joe and Clearwater River basins of northwest Montana and northern Idaho. Acreage by Section 20-M333A 17,556 LTA Setting and General Characteristics Differentiating characteristics: This map unit occurs primarily at low to mid elevations, on steep slopes adjacent to stream drainages. Parent materials are surface volcanic ash overlying weakly to moderately weathered quartzites, siltites and argillites from Precambrian metasedimentary bedrock. In Montana surface ash may or may not occur. Accessory Characteristics: The primary soils are shallow to deep loams and sandy loams, with a small to moderate component of rock outcrop and scree. The vegetation is a mosaic of coniferous forest. Mean annual