 The <unk> Creek Mountains are composed mostly of basalt from a shield volcano that once stood where <unk> Mountain is today . <unk> thinning and the Yellowstone <unk> , which was then beneath southeastern Oregon , induced eruptions from <unk> and nearby <unk> about 17 million years ago , in the Miocene . The <unk> produced a series of <unk> flows that spread across the land now known as the <unk> Creek Mountains . <unk> from the <unk> volcano lasted for about one million years , and at least 70 separate <unk> flows occurred . Under the resulting basalt rock lie much older <unk> rocks that may be related to some of the <unk> age formations of the Blue Mountains in northeastern Oregon . Within these <unk> rocks are <unk> and <unk> <unk> bodies which were presumably <unk> during the Cretaceous Period . 
