Between Baker City, Oregon and Sumpter is a range of Mountains called the Elkhorns. The south most pass is the Marble pass. The picture above is from the top of the pass looking west. You can see the white patch below that is the limestone mine. Note the location on the map below. The blue circle highlights the white area near the crest of the pass that is an old limestone/marble quarry. It is best to access this area from the Sumter side of the mountain. The road up the canyon from Baker City following Marble Pass Creek Road is miserable--lots of creek crossings, big boulders, low hanging brush, steep. The road from the Sumpter side comes out just east of Sumpter at McEwen.
The road up is dirt/gravel and in pretty good condition for a high wheel clearance vehicle. The last mile or so to the pass can be washed out in places, but you need not go to the top to get to the mine.
The mines are open pit with some shafts cut into the walls of rock, There is plenty of material here. The challenge is to get a large solid piece that is not checked with cracks.
Some of the marble found here is not particularly hard. The black and white spidery veined variety is rather soft, but it does polish well and makes good box tops and book ends. There are some spots where the marble is very hard , but the colors are brown to green and may not be as showy.