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California State Route 172

After using CA 32 to get to the junction of CA 36/89 I took CA 89 to Lassen Volcanic National Park.  On the way out the south exist I pulled off on CA 36 west and took it to the junction of CA 172.






CA 172 is a 9 mile loop to/from CA 36 from Mineral to near Mill Creek in rural Tehama County.  Much of CA 172 is a one-lane state highway over Mineral Summit and was once the original alignment of CA 36.  I started out from CA 36 in Mineral and headed eastward on CA 172.  CA 172 from the western terminus starts out as a one-lane highway.





CA 172 eastbound travels through a small valley before ascending into the mountains.  Interestingly it is actually kind of vague whether the range CA 172 occupies is the Sierra Nevada or Cascade, but I'll touch on that in a bit.


I didn't encounter another vehicle on CA 172, most of the one-lane portion of the highway actually closes for the winter.  The climb to Mineral Summit is fairly straight-forward although a little rougher than the typical one-lane state highways I've encountered in the past.



The descent to Mill Creek at 4,737 is fairly tame given there isn't much of an elevation drop.  Mill Creek is the name of a community and also a creek which CA 172 begins to follow east from Mineral Summit.  You know you're approaching Mill Creek when the "35 MPH Zone Ahead" sign is observed.  Kind of amusing to think that all the one-lane highway westward to Mineral is actually an unsigned 55 MPH zone.





East of Mill Creek CA 172 widens out to a normal length but never gets a center stripe.  CA 172 quickly ends at CA 36/172.








Most state highway maps generally don't show the detail necessary to see when CA 36 shifted from the alignment of CA 172 northward.  The current route of CA 172 was once part of Legislative Route 29.  Current CA 36 east of Mineral to CA 89 was part of LRN 86 and CA 36/89 was part of LRN 83.  Originally CA 36 was signed on all of LRN 29 from Peanut east to US 395.  For reference all the old LRN designations can be seen on the 1963 State Highway Map.

1963 State Highway Map

By the 1964 Highway Renumbering all the modern route alignments had been designated and LRN 29 over Mineral Summit was renumbered to CA 172.

1964 State Highway Map

What isn't exactly clear is when CA 36 jumped from LRN 29 east of Mineral onto LRN 86/83.  The 1935 Tehama County Map by the California Division of Highways shows all three LRNs existing at the time as state maintained roadways.

1935 Tehama County Highway Map

USGS Maps show that CA 36 had made the jump north to LRN 86/83 by 1956.  The 1956 Map in question can be found at the following link by searching for "Mineral, CA" and looking up Lassen Peak Map of the same year.

http://historicalmaps.arcgis.com/usgs/

The 1962 Map from Susanville also shows CA 36 routed over LRN 86/83 while the 1935 Paynes Creek Map has it on LRN 29.  The narrowest window for the alignment shift for CA 36 off of LRN 29 I can find therefore is between 1935 to 1956.  Odd to consider that such an outdated segment of state highway like CA 172 has somehow managed to survive the years and is still signed in the field.

Interestingly CA 36 over Fredonyer Pass and Morgan Summit is generally thought to be the boundary point for the Sierra Nevada Range and Cascade Range.  Generally the way the Range boundary is cited is not the names of the passes but rather by CA 36.  I'm not aware of CA 172 nor Mineral Summit being called the boundary of the Sierra and Cascade Ranges but it would be reasonable to assume that it likely was considered to be before CA 36 was realigned.

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