 The highest point in the hills (as well as Benton County) is the Lookout Summit, which surpasses the more well-known Rattlesnake Mountain by approximately 100 ft (30 m).The Rattlesnake Hills are part of the Yakima Fold Belt of east-tending long ridges formed by the folding of Miocene Columbia River basalt flows.The Rattlesnake Hills form the northern edge of the Yakima Valley, running from the vicinity of Benton City to just south of the city of Yakima, where the Yakima River cuts through the mountain ridge via Union Gap.