From Las Vegas take I-15 north for 22 miles. At exit 64 take US-93 north. After 85 miles, 12 miles past Alamo, you come to the intersection with Hwy. 318 on the left. Directly across the road from the intersection, to your right, you will see the remains of an old casino.
At the intersection turn left onto Hwy. 318, and after less than a mile veer left again onto Hwy. 375. At that intersection you will see the "Extraterrestrial Highway" sign under a group of trees on the right. From here it is about 40 miles north-west to Rachel.
The last gas in Las Vegas is at the intersection of I-15 and US-93. There are a couple of gas stations on the way, in Alamo and Ash Springs. There is no gas in Rachel, or anywhere along the 150-mile stretch between Ash Springs and Tonopah. Also, some of the gas stations close at night. So you may want to keep an eye on your gas.
Please note that most of Hwy. 375 is open range. There are no fences, and cows frequently wander across the road. When you see cows near the road slow down and be prepared to stop. Be especially careful at night, when cows on the road are very hard to see. Running into a cow will not only cause severe damage to your vehicle, but you will also have to reimburse the rancher for the cow. And it is usually his most expensive cow...
For a more detailed map of the Rachel / Groom Lake area click here.