Rockfall hazard on steep rock slopes is strongly controlled by the geometry of in-situ blocks bounded by intersecting discontinuities. In practice, however, source blocks are still commonly identified by field observation and manual interpretation, which is difficult to apply consistently on high, steep slopes. This study develops a three-dimensional point-cloud-based workflow for locating, characterising, and assessing potentially unstable rock blocks under real terrain conditions. The approach combines structural interpretation with visual kinematic criteria to detect discontinuity combinations associated with planar sliding, wedge sliding, and toppling, and to map unstable blocks directly in point-cloud space. Block volumes are then estimated by point-cloud differencing, allowing the number and size distribution of source blocks to be described quantitatively. Finally, representative blocks are introduced into three-dimensional rockfall simulations using their measured location and volume. The simulations provide rockfall frequency, bounce height, velocity, and kinetic energy, and are used to evaluate the threat posed to the transportation corridor below the slope. The proposed workflow links source identification with dynamic hazard assessment and offers a practical basis for rapid screening and refined mitigation of rockfall-prone slopes in mountainous infrastructure corridors.