 The broad <unk> <unk> is a prominent geologic feature in the <unk> Creek Mountains . The oval @-@ shaped <unk> is a collapsed <unk> dome that <unk> the Oregon – Nevada border on the eastern side of the range and south of the Oregon Canyon Mountains . It is about 28 miles ( 45 km ) long and 22 miles ( 35 km ) wide . The <unk> dome was created by volcanic eruptions in the early Miocene . A total of five large ash flows were produced along with a large <unk> dome structure . The <unk> formed when the dome collapsed about 16 million years ago . The <unk> contains significant ore deposits , and mercury and uranium have been mined at eight or more sites in and around the <unk> . Other areas in the <unk> were mined for ores of antimony , <unk> , and lithium . 
