Descriptions:
Changelog v15.1

US-101 widened all the way to Oxnard (Agoura Hills/Thousand Oaks area)
A little more urbanization east of the I-10/I-15 interchange (San Bernardino/Redlands/Calimesa)
Signage update across all covered California area, plus new signage on I-40, CA 58, CA 99 and I-10 east of San Gorgonio Pass (The map in the OP has been updated, if you want to visualize that better)

I-5 widened to 2×4 from San Diego to just north of Los Angeles (originally a mix of 2×2 and 2×3)
I-5 narrowed to 2×2 from Sacramento to Redding (originally 2×3)
I-10 widened to 2×4 from Los Angeles to Palm Springs (originally 2×3 and 2×2)
US 101 widened to 2×4 in the Bay Area and near Los Angeles (originally 2×2 and 2×3 respectively)
I-580 (the California one) widened to 2×4 from the I-5 junction to Richmond (originally 2×2)
I-80 widened to 2×4 from Richmond to SR37 and 2×3 up to Sacramento (originally 2×2)
CA-99 widened to 2×3 near Bakersfield and 2×4 in Bakersfield (originally 2×2)
Some very minor signage changes, mostly getting rid of “Carlsbad” being posted everywhere.
Areas near Los Angeles, the SF Bay area and Sacramento more “urbanized”
Downtown Los Angeles remodeled.

Fresno,
CA-99 is done up to halfway to Fresno and vanilla signage has been
replaced with the post-Arizona sign templates in the Los Angeles area
and the reworked CA-99 area. Had to take some artistic liberties in some
places due to how different the road network is in the game compared to
real life.

Authors:
Quaristice

Download Link 2: Download mod