Wikipedia:WikiProject U.S. Roads/Idaho/highway names

Most information is from the meeting minutes and 1923 and 1925 maps (the latter bolded below).
 * Alexander-Lund-Bancroft Road
 * Ammon Spur: Idaho Falls to Ammon, removed 1953
 * Arrow-Deary-Harvard Highway? SH-42: Spalding to Harvard
 * Ashton-Drummond-Tetonia Road SH-32
 * 32 Bannock Highway SH-38: Holbrook to Pocatello
 * 36 Bear Lake Highway SH-35: Utah to Montpelier
 * Beeches Corner South Road
 * Bellevue-Gannett Highway
 * Boise-Stanley Highway SH-21: Boise to Stanley
 * Former 1 Arrowrock Highway: Boise to Arrowrock
 * Former 35 Forest Highway: Lowman? to Stanley
 * Boise Valley Highway: included Desert Junction-Middleton
 * Bruneau-Duck Valley Highway
 * Buhl-Castleford Highway SH-73: included Buhl southwest
 * Canyon Highway SH-4: Wallace to Montana
 * 3 Camas Prairie Highway? SH-13: Grangeville to Kooskia
 * 5 Clark Fork Highway SH-3: Sandpoint to Montana
 * 6 Clearwater Highway SH-11: Greer to Montana
 * 23 Coeur d'Alene-Yellowstone Trail US-10: Washington to Montana
 * Craigmont-Kamiah Highway?? SH-12: Craigmont to Kamiah
 * Former 24A Nez Perce Branch of the North and South Highway: Craigmont to Nezperce
 * Colburn Culver Road (SH 55):
 * Cooley Road
 * Cotton East Road
 * Cub River Road
 * Dayton-Red Rock Road (SH 35): included Oxford-Red Rock
 * Deary-Bovill Road
 * Declo-Albion Highway, formerly 4 Cassia Highway SH-77: Albion to Declo
 * Dufort Road
 * East Branch Road SH-57: included Priest River-Coolin
 * East-West Road? included Fairfield
 * 7 Elk City Highway SH-14: Harpster to Elk City
 * 8 Elk River Highway SH-7: Orofino to Santa
 * 34 Elk River Extension SH-7: Nezperce to Orofino
 * Enaville-Murray Highway
 * Fairfield-East Road
 * Fairfield-West Road
 * First Street-Iona Road
 * Genesee-Thorn Creek Road?
 * Georgetown-Nounan Road
 * Glenns Ferry-East Road
 * Gooding-Fairfield Road?
 * 10 Grace-Preston Highway SH-34: Preston to Alexander
 * Grace-Turner Road
 * Grangeville-Craigmont Road
 * Grangeville-Harvard Highway: included Harvard-Deary
 * 11 Gray's Lake Highway SH-34: Soda Springs to Wyoming (earlier Soda Springs to Idaho Falls)
 * Green Creek Junction-Reservation Line Road
 * 12 Heyburn Park Highway SH-5: Plummer to St. Maries
 * 13 Idaho Central Highway SH-22: Mountain Home to Trude
 * 14 Idaho-Montana Highway US-91: Idaho Falls to Montana
 * 15 Idaho-Oregon Highway SH-19: Oregon to Caldwell
 * Ketchum-Clayton Highway (appears to be another name for part of the Sawtooth Park Highway)
 * 38 Kootenai Highway US-2: Bonners Ferry to Idaho
 * 18 Lemhi Highway SH-28: Roberts to Salmon
 * 19 Lewis and Clark Highway SH-9: Washington to Montana
 * Lewiston-Orchards Road is another name for Thain Road.
 * 20 Lost River Highway SH-27: Challis to Moreland
 * 21 Malad Valley Highway SH-36 &rarr; US-191: Utah to Downey
 * McCammon-Robin Road: included Robin-Arimo
 * Middleton-South Road
 * Minidoka-Kimama Road?
 * Montour-Ola Road: included Sweet-Ola
 * 22 Moscow-Bovill Highway SH-8: Moscow to Bovill
 * Mountain Home-Grandview Road: included Grandview east
 * Nampa Road: included Boise-Nampa (US 30)
 * Nez Perce Highway SH-62: included Craigmont-Mohler
 * North Bench Road
 * 9 North Side Highway SH-25: Gooding to Rupert (earlier Declo?)
 * 24 North and South Highway US-95, US-95A: Weiser to Canada
 * Copeland-Porthill Branch SH-1: Copeland to Canada
 * North Yellowstone Highway?
 * 16 Old Oregon Trail Highway US-30, US-30N: Oregon to Wyoming
 * 17 Ontario Branch US-30: Oregon to Fruitland
 * 40 Southern Branch US-95, SH-18: Fruitland to Blacks Creek
 * 41 Bancroft Loop: Lava Hot Springs to Lund
 * 33 Oneida Highway SH-37: Malad to American Falls
 * Ora Road: included west from Ashton
 * 25 Owyhee Highway US-95, SH-20: Oregon to Nampa
 * 37 Palouse Highway US-95: Potlatch to Coeur d'Alene
 * Parma-Wilder Highway
 * 26 Payette Highway SH-15: Boise to New Meadows
 * Emmett Branch SH-16: Emmett to Horseshoe Bend
 * Payette-Emmett Highway SH-16: Payette to Emmett, branch to New Plymouth
 * Former? Emmett-New Plymouth Highway: Emmett to New Plymouth
 * Pine Creek Road
 * Pingree-Thomas Road
 * Preston-Bear River Highway
 * Priest River Road SH-57:
 * Reservation Line Road
 * Rexburg-Parker-St. Anthony Road: included Parker south
 * Ririe-Beeches Corner Road
 * Roberts-Ririe Highway SH-48: Roberts to Ririe
 * Roberts West Road
 * Robin West Road
 * Rock Creek Road (SH 47): east of Ashton to Wyoming (Cave Falls Road), removed 1951
 * 27 Roosevelt Highway SH-24, SH-39, SH-29: Bliss to Wyoming
 * Former 2 Bliss-Shoshone Highway: Gooding to Shoshone
 * Round Valley-Cascade Road
 * Sagle-Midas Road (SH 56):
 * Salmon River Highway?
 * Salmon River North Highway?: included Riggins-Whitebird
 * Samaria Lane Road
 * 28 Sawtooth Park Highway US-93: Nevada to Montana
 * Blue Lakes Spur: Kimberly Road to Addison Avenue in Twin Falls, created 1953
 * Richfield Branch SH-23, SH-22: Shoshone to Bellevue
 * Richfield Spur (SH 76):
 * Twin Falls Loop SH-26: Godwin to Twin Falls
 * Schiller-Arbon Valley Road?
 * Sharon-Ovid Road
 * Shelley-New Sweden Road
 * South Yellowstone Highway SH-33: Rexburg to Wyoming
 * Spirit Lake Highway SH-41: included Ross Point-Rathdrum
 * 39 State Line Highway SH-40: Wyoming to Wyoming via Geneva
 * 29 Teton Highway SH-32: Tetonia to Ashton
 * Thain Road: Lewiston to Richardson Avenue, removed 1951
 * Tin Cup Road
 * Triumph Mine Road: Gimlet east, removed 1951
 * 30 Twin Buttes Highway US-20: Arco to Idaho Falls
 * Ucon-West Road
 * Victor-Irwin Highway
 * Wapello to Firth Road
 * Wayan to Freedom Road
 * Wood River Road
 * Worley-State Line Highway SH-58: Washington to Worley
 * 31 Yellowstone Park Highway US-91, US-191: Utah to Montana
 * Yellowstone-Sun Valley Highway

What was the name of SH-6, Washington to Potlatch?