Elk are relatively recent immigrants to North America, at least in geological terms. Elk migrated to North America over the Bering Land Bridge approximately 120,000 years ago under a period when much of the world's water was locked in glaciers.

Archaeological evidence suggests that elk inhabited these areas over the past 10,000 years; however, they were gone from the area by the mid-1850s, based on discussions and writings of Native Americans, early explorers and settlers. Following their extirpation from Washington, the area was devoid of elk for several decades until the 1930s, when Rocky Mountain elk were brought from Yellowstone National Park in Wyoming and reintroduced to Washington in the Cascade Mountains near Mt. Rainier. Elk were first seen on the Monument in 1972. This original group of animals was believed to originate from the Cascade Mountains to the west and arrived naturally. Since approximately 1975, the Rattlesnake Hills Elk Herd core range has been the Arid Lands Ecology Area on the Monument and private land to the south and west. Peripheral rangelands include the Hanford Site, the Rattlesnake Hills west of State Route 241, the Yakima Training Center, and southern Grant and western Franklin Counties.

There were six subspecies of elk in North America (two are extinct). Rocky Mountain elk are native to the Columbia Basin and the Hanford Reach National Monument; the elk on the Monument are Rocky Mountain elk.

Prior to the 1800s, elk lived in every state and province except Alaska and Florida. Today, their range has been reduced to 24 states and seven provinces. Approximately one million elk live in North America today—10% of the population before European settlement. Washington has the sixth largest state elk population, with approximately 60,000 elk (Rocky Mountain and Roosevelt elk).

Elk are amazingly adaptable and can live almost anywhere—forests, deserts, mountains, and plains. They eat a wide variety of plants. Their typical diet consists of grasses (year-round), woody plants (winter) and forbs (summer).

Elk are majestic animals. Cows typically weigh no more than 500 pounds, but bulls can reach 700 pounds and stand 5 feet at the shoulder. Only bull (male) elk grow antlers. Grown annually to display dominance for breeding, a pair of antlers can weigh up to 40 pounds.

Elk mate in autumn. Calves are born 8-1/2 months later, from mid-May through early June, depending on location. Newborn calves weigh 35 pounds, and although newborn calves can walk with their mothers within a couple of days of birth, they usually stay hidden for the first couple of weeks of life. Newborn calves have almost no scent to avoid attracting predators as they lay hidden in thick brush or tall grass; white spots help to camouflage the calf by breaking up its outline and mimicking spots of light.

Rarely seen in the summer when they “head to the hills,” in the winter elk are frequently seen from Highway 240. If you're lucky, you might see these majestic animals from your car. But please be careful if you stop to view them as there is only one designated pull-out along the highway, and traffic can be quite heavy when the shift ends on the Hanford Nuclear Reservation.

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