College of Southern Nevada history professor Michael Green explains, "If you look at downtown, you’ll notice that the plat (or layout) is at an angle to the Strip, beginning roughly at the point where Main Street, Las Vegas Boulevard, and St. Louis Avenue converge, just north of the Stratosphere. Because of the terrain of the Las Vegas Valley, it was easiest to run the railroad line from southwest to northeast, through what became downtown."
The old road in from California, now Las Vegas Boulevard, runs due north as far the Forum Shops. If it had continued on that course, it would have crossed the railroad out back of Circus Circus and bypassed downtown completely. Instead, as it neared the railway, it altered course and parallels the tracks into downtown. If you want to approximate where a hypothetical straight-line Strip would have eventually headed, take Sahara Avenue west from Las Vegas Boulevard, across I-15 to Rancho Drive, then turn right and keep on heading north, until it turns into Tonopah Highway.
So if you’ve puzzled at why downtown Las Vegas sits at an angle to the valley’s north-south grid, blame the railroad barons. They got there first and literally set the pattern for the future of Sin City.