Getting back to even more obscure CA state highways, there's always CA 172, tucked up in the mountains south of Lassen Park. Interesting history -- this about 12-mile loop was the original LRN 29, the primary route east of Red Bluff to Susanville and then on to Reno, NV, and, before about 1934, was signed as SSR 36. That section, between Mineral and Morgan Summit, was routed through a narrow valley -- one that just happened to feature numerous lodges and spas built to take advantages of the numerous hot springs in that volcanic area. It zig-zagged back and forth across the valley, serving the various facilities -- but because of the constricted space in the valley, the roadway was never more than 18 feet wide -- and was never striped for 2 lanes. In 1934 the route was bypassed by LRN 86, which was laid out in a large S-curve from Mineral (the present west junction of 36 & 172) to LRN 83 (SSR 89) south of the southern entrance to Lassen Park; while not much of a saving in total mileage, it was a more modern 2-lane facility that not only allowed faster speeds but also cut about 13 miles off the distance between Red Bluff and Lassen Park. SSR 36 was rerouted over LRN 86 when it was completed, leaving the LRN 29 loop unsigned until the '64 renumbering, when it was signed as CA 172.
Back about 30 years ago one of my many cousins in the Sacramento area planned a large family reunion and selected the hot-springs resort in Mineral as the location. My then-wife and I drove up there, using CA 32 up the hill from Chico. Once up the hill, I decided to use CA 172 to get to Mineral (just to clinch it, although I told my wife it would probably be more scenic!). It was still one lane -- actually narrowing to about 13-14 feet in some sections -- and would have been fine except for one thing -- some event was happening in Mill Creek, and there were hundreds of cars and trucks backed up on 172 trying to get into a small dirt access road. It took us nearly an hour to go the 12 miles to Mineral (my wife wasn't terribly happy about that; the phrase "scenic, my ass!" pretty much said it all). Overall, not one of the better road trips in memory. My overall assessment of 172 was that it was a unique (any one-lane state highway fits that description) short route, but one that certainly was of little use as a through facility. I understand decommissioning of 172 has been under discussion for several years now, but the plug hasn't been pulled as of yet (probably due to objections by the several property owners along the highway who want to make sure it gets plowed in winter; it's at about 5700-6000 foot altitude).