This climb is one of many at the Peshastin Pinnacle State Park. This is not "well protected", but not without protection. The Belay stations are very protected with bolts. This was very challenging for our level of climbing. Very enjoyable.
Martian Slab is the second main pinnacle from the parking lot, more to the east side of the park. Just walk through the gate and head up the trail to the climbin area.
Martian Diagonal is described well in the Leavenworth Rock book, along with many, many other routes at this location, with excellent photos. However, this route follows an "obvious" diagonal line across the main southern face of Martian Slab, the second main pinnacle at this State Park as viewed from the parking lot. The starting point of the first pitch has several choices, but the main diagonal line is the first goal, with two good bolts and hangers with a nice built in seat for your belay about 75 feet from ground zero, depending on where you start. Climbing to this first belay point had the difficult moves for us. From this belay, you are on the ramp or diagonal break, passing one old piton and bolts going another 120 feet plus to another belay point needing your own gear (slings and cams) to belay from. You only have a short ridge, 50 feet plus, where you can rappel down in several directions. We rappeled down the south slab about 100 feet.
One or two ropes of at least 50 meters, depends on your descent route choice. We use two so we could rappel where we wanted without worrying if the rope would reach the ground. There are several bolts with hangers, but we used slings and cams for anchors on top and quick draws on the way up.