Back in 2015 and 2016 I visited the South Rim of Black Canyon of the Gunnison National Park via CO 347. CO 347 apparently was added to the state highway system in 1939 but the road definitely existed before then. South Rim Drive is 7 miles in length and is the continuation of CO 347 along the top of Black Canyon. Black Canyon of the Gunnison National Park may be small by NPS standards but I found it to be an interesting drive with some really scenic short hikes:
https://www.gribblenation.org/2020/03/2016-summer-mountain-trip-part-21.html