The impact force from a granular sliding mass on a rigid obstruction can be used to gain insights into the granular flow; however, such data is remarkably scarce in the literature. In this study, a two-dimensional soil flume was constructed and utilized to measure the impact force from a granular sliding mass on an obstruction instrumented with dynamic load cells in order to systematically study the effects of different factors on the impact force. In this paper, the effects of initial soil density and inclination angle on the impact force were investigated. Results from these experiments showed that in gentle slopes (i.e., low inclination angle) as the initial density increases the impact force decreases. However, in steep slopes (i.e., high inclination angle) when densely packed granular mass flows downslope with high velocity, the flow is similar to the sliding of a less-deformable block and the impact force increases as the initial density increases.