It is the major formation in the Breezy Point Area of Rushmore. Sentinel Rock in co-located, just to the NE of Lost Arrow Spire and BB. It provides a spectacular view of the range in all directions.
To access Lost Arrow Spire, BB, and Sentinel Rock: Park at the Breezy Point Parking Lot, follow the sidewalk to the NW for 60' until the sidewalk curves up and left. Depart the sidewalk and gain the old road bed and follow it for 300' until the road curves sharply to the left. There is a single track trail located at the curve that descends down from the road, follow this for 25' to intersect another trail on the left that follows the drainage down. Take this for approx 300' to the base of Lost Arrow Spire, BB, and Sentinel Rock on the south side of the formations.
Sentinel Rock is the major formation of the 3; located to the NE of Lost Arrow Spire and BB.