On county maps of California, an oddly straight horizontal line bisects the state about 30 miles north of Bakersfield.

In perennial debates over where Southern California ends and Northern California begins, no official answer exists and opinions vary widely.

But it was based upon this line — comprising the northern boundaries of San Luis Obispo, Kern, and San Bernardino counties — that California came closer than ever to actually splitting into two.

In 1859, Southern Californians upset by taxes and land laws pushed the Pico Act to lop off the state’s southern counties and create a proposed “Territory of Colorado.”

The new territory would stretch from the Mexican border to an east-west line along a land grid established by the U.S. General Land Office.

The grid spread across California based on a few geographic anchor points, including the Bay Area’s Mount Diablo. The northern border of the new territory, the Pico Act proposed, would fall along a line of latitude six standard parallels — or intervals spaced 24 miles apart — south of Diablo.

The state Legislature, the governor, and nearly 75% of voters in the proposed territory endorsed the partition plan before it was derailed by the opening of the Civil War in 1861. California would remain intact.

But the prominence of the sixth standard parallel endured. As California settled its county borders over the next couple decades, it drew a boundary line that traced the parallel across the width of the state. The resulting map created a visual reminder of a cultural divide between north and south that was never quite erased.

More from the California Sun

• California Sun readers share feedback on the newsletter
• Photos: Rare September snow dusts June Lake in Eastern Sierra
• Highway 1 used to be a wooden boardwalk for cars
• Swooning over San Francisco’s Tetris house
• The strange boundary line that divides California in two

Get must-read stories about California your inbox each morning . Sign up here