A good road is a good road - many modern highways (and railroads) follow old wagon trails west. The Santa Fe Trail, for one, begins in Independence, MO, (Kansas City on your map) heads south to Wichita, and from there follows your arrow first west and then south (although the actual trail veers south before Pueblo, CO). The Santa Fe Trail ended in (wait for it) Santa Fe, NM, at which point your trail connects with the Camino Real to Albuquerque. There, your arrow turns west again, following what is today I-40 and what was Route 66. The railroad still follows this path, as does I-40 (mostly) into California. However, this road was pioneered in the 1850s by a man named Edward Fitzgerald Beale, who was commissioned by the War Department to not only determine if a road following the 35th Parallel was feasible, but also to see if, given the area's arid nature, camels would be useful to the Army. The route would become known as Beale's Wagon Road and while I-40 does follow parts of it today, parts are also unused except for hiking, where ruts are still visible in the dirt. The camels proved very useful and hardy - Beale reported that they could carry heavier packs than the other stock, drank almost nothing, and seemed to prefer saltbush and other shrubs that horses, burros, and mules avoided. When crossing the Colorado River, all the camels plunged in fully loaded and uneventfully swam across; two horses and ten mules drowned. Beale even learned Arabic so as to "speak to them in their native language" and hired a Turkish herder named Hadji Ali to assist him. He was universally known as "Hi Jolly" and immensely popular - check out the memorial at his grave the State of Arizona put up. Beale recommended the War Department purchase 1,000 more (up from an initial 33), but the horses, donkeys, and mules (as well as dogs) were afraid of the spitting beasts, and the outbreak of the Civil War ended the Camel Corps' funding, not to mention the mule lobby's anti-camel efforts. The animals were auctioned off (Beale and Ali both bought several), and some eventually escaped (or were released), and feral camels were seen in Arizona into the 1940s.

Getting back to your trails, the one running through Nebraska and then southern Wyoming is approximately the Oregon Tail. Just past the South Pass of the Rockies (in truth not quite as far west as Salt Lake City, but close enough) the route diverges with the Oregon Trail heading northwest to (drumroll) Oregon and the California Trail bearing west through Nevada to, believe it or not, California. There's also a southern route from Salt Lake; that's the Southern Route. JK! But not really - it's more commonly called the Mormon Road to Los Angeles and today I-15 follows most of it. Then that southern, swooping arrow out of Las Vegas follows the Colorado River until it hits the old Butterfield Overland Mail Route and Juan Bautista de Anza Trail, although I'm not familiar with a particular trail also following the river.

The Oklahoma/Texas to El Paso route follows Route 66 (and again, Beale's Wagon Road), but I'm not familiar with that route running south through the Llano Estacado. I initially thought it may follow the Goodnight-Loving cattle trail, but that's further west in New Mexico and as far as I can tell no roads mirror it today. I'm afraid I can't help you at all with that nothernmost one, however, but thanks for giving me a chance to talk about Ned Beale and the Camel Corps.