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Alameda County architect Henry H. Meyers designed four Art Deco medallions featured on the face of the original 1937 Caldecott Tunnel as seen in this photograph made Wednesday, Feb. 1, 2012, in Oakland, Calif. A matching set of medallions also grace the Orinda portal. A contest will decide what new medallions will grace the Caldecott Tunnel fourth bore. (Karl Mondon/Staff)

Today marks the 75th anniversary of the opening of the Caldecott Tunnel between Oakland and Orinda, an important gateway between Contra Costa and Alameda counties.

The first two bores -- each two lanes -- opened Dec. 5, 1937 to much fanfare.

Fireworks and a speech by Gov. Frank Merriam highlighted ceremonies on the Oakland side. During ceremonies on the Orinda side, cars lined up for miles to make the first westward trips through the tunnel.

The original two bores cost $4.5 million and took three years to build. They replaced a single-lane 1903 tunnel that was prone to closing due to flooding and mudslides.

A third Caldecott bore opened in 1964, making it possible for the middle bore to reverse directions daily to meet demand during the morning and evening commutes.

Contractors hired by Caltrans are building a fourth bore scheduled to open in late 2013, said Caltrans spokeswoman Ivy Morrison.

When the two lanes in the new bore open, the Caldecott Tunnel will have four lanes in each direction all the time.

Contact Denis Cuff at 925-943-8267. Follow him at Twitter.com/deniscuff.