Former US Route 99 in Dunsmuir of southern Siskiyou County, California was located on Dunsmuir Avenue. Pictured above is former US Route 99 on Dunsmuir Avenue in downtown Dunsmuir as it appeared in the September/October 1951 California Highways & Public Works. Below is a image from the 1935 Division of Highways Map of Siskiyou County which depicts US Route 99 on Dunsmuir Avenue.
Part 1; the history of US Route 99 in Dunsmuir
The first documented European travel through the present site of Dunsmuir and Sacramento River Canyon came in 1828 when it was explored by Hudson Bay trapper Alexander McLeod. The travels of Alexander McLeod through Alta California established what came to be known as the "Siskiyou Trail" between what is now Oregon and California by way of the Sacramento River Canyon. The present site of Dunsmuir later became part of a major 1837 cattle drive to Oregon along the Sacramento River Canyon via the Siskiyou Trail. The 1837 cattle drive was followed by a 1841 mapping survey of the Sacramento River Canyon which documented much of the path of the Siskiyou Trail. The Siskiyou Trail would become a major path of emigrant travel following the finding of Gold at Sutter's Mill in 1848 and the emergence of the State of California during the California Gold Rush.
Gold was discovered at what became the City of Yreka in 1851 which was followed by numerous other claims in Scott Valley. The formation of the California-Oregon Trail saw much of the Siskiyou Trail in the Sacramento River Canyon bypassed to the west via; Scott Valley, Scott Mountain and the town of Shasta. Nonetheless the Sacramento River Canyon and Siskiyou Trail remained an established path of travel. In 1855 a tolled bridge over the Sacramento River was built at Upper Soda Springs immediately north of modern Dunsmuir by settlers Ross and Mary McLeod. The Siskiyou Trail would be improved by 1860 to a road capable of handing Stage Travel from Upper Soda Springs to Yreka and southward through the Sacramento River Canyon by 1870. Upper Soda Springs in time became a stage stop and resort which catered to travelers on the Siskiyou Trail. The Upper Soda Springs resort can be seen circa 1875-1880 in the public domain drawing below.
Thusly US 99 appears on the 1925 Rand McNally Map of California as being routed through Dunsmuir via Florence Avenue.
As noted in the intro the 1935 Division of Highways Map of Siskiyou County depicts US 99/LRN 3 along Florence Avenue.
The January/February 1948 California Highways & Public Works announced US 99/LRN 3 in Dunsmuir was slated to be converted to a freeway.
The reconstruction of US 99/LRN 3 in the Sacramento River Canyon along with much of it's history as a transportation corridor is discussed in the May/June 1956 California Highways & Public Works. The first contract to rebuild US 99/LRN 3 in the Shasta River Canyon came in 1952 which was for 4 miles of divided highway north of Dunsmuir. This was followed by a new contract in 1953 to construct a new bridge over the Sacramento River in Dunsmuir. 12 miles of US 99/LRN 3 north from Redding to Shasta Lake City were cited to have been completed in 1955. The article goes on further in terms of describing three ongoing contracted projects in the Sacramento River Canyon which included a new bridge over Dog Creek and 6.5 miles of additional highway. Surveys for reconstructing the remaining 19 miles of US 99 between Shasta Lake and Dunsmuir were cited to be underway.
The May/June 1958 California Highways & Public Works cites that 6.9 miles of new divided highway for US 99/LRN 3 in the Sacramento River Canyon from near Lamoine to the vicinity of Shotgun Creek was under construction.
The AASHO database shows that US 99 was approved to be truncated out of California by the AASHO Executive Committee on June 29th, 1965. This measure would have become effective on New Years Day 1966 and made the freeway bypass of Dunsmuir solely part of Interstate 5.