Route 242 is from Route 680 to Route 4 north of Concord. [CS&HC Sec. 542]

1964-1991: Route 242 signed as Route 24 (as I have long suspected). Older signs for Route 680 between Routes 24 and 242 had greenouts on them suggesting this.

1991: Portion (b) of Route 24 is defined as a separate bypass around Walnut Creek to Pittsburg.

Entire route. [CS&HC Sec. 253.1]

Entire route.

Route 680 to Route 4: Terminal Access.

At 3.4 miles, Route 242 is a quaint suburban thoroughfare. Clayton Boulevard is the main exit to Concord, home of the world-famous Blue Devils Drum Corps. A BART Station is located on Clayton.

This following bit is from fellow highway enthusiast Willis Lamm about Route 242:

"Also, your theory regarding Route 24 / 242 is correct. In the mid 1970s Route 24 between I-680 and Route 4 was renumbered Route 242. There was just too much confusion regarding the two nearby interchanges of the two original Route 24s and I-680. The local joke about the renumbering when motorists with out of date maps got confused and asked directions was, 'Yes, that's Route two-four-too.'"

Here's more from another highway enthusiast, Michael Murray:

"That, however, is not the whole story. At one time, R24 was to follow a proposed freeway to be built alongside and in place of Ygnacio Valley Road, which starts at the I-680 in Walnut Creek and runs through Walnut Creek and Concord. Leaving Concord, the route continues as Kirker Pass Road, leading to Pittsburg, where the freeway was to connect to R4 at Loveridge Road, I believe. Citizens of Walnut Creek killed this freeway, however, in a referendum in the early 70s. Today, the Kirker Pass / Ygnacio Valley corridor is a mjor commute link, handling huge volumns of traffic."

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