Following the San Gabriel River, sometimes right along its banks, this freeway forms a decent bypass of the central Los Angeles area. It also has the unique aspect of having no real control cities on the mainline. All the signs point to “Thru Traffic” instead of a city. This may have been done as a test, though that test has long since ran its course. The freeway was built between 1964 and 1966. The norther end, from I-10 to I-210 was the last section and was completed in 1971.
Visible signs that the I-605/SR-22/I-405 interchange was built with a southern extension of I-605 in mind. The 405 mainline is in the upper right corner, the 605s to 405s connector coming out of the tunnel, the 22e to 605n/405n connector on the right, and the 405s/605s to 22w connector on the left.