Consisting primarily of basaltic andesite , it has a more mafic composition than the other two volcanoes .
North Sister is 5 miles ( 8 km ) wide , and its summit elevation is 10,090 feet ( 3,075 m ) .
Consisting primarily of basaltic andesite , North Sister has a more mafic composition than the other two volcanoes .
North Sister is 5 miles ( 8 km ) wide , and its summit elevation is 10,090 feet ( 3,075 m ) .