Abstract: In recent years, high-elevation collapses have occurred frequently in the Wumeng Mountains, posing severe threats to lives and property in the region. It is therefore essential to enhance the understanding of the dynamic processes associated with such disasters. This study takes the Longjiayanjiao high-elevation rock collapse that occurred in June 2024 in Nayong County, Guizhou Province as a case example. We analyzed the characteristics of the collapse deposits through field investigations and UAV-based image recognition, and simulated the collapse dynamics using LPF3D (Landslides Post Failure 3D), a self-developed SPH–SDPH–DEM coupled numerical modeling software. The results show that: (1) The movement path, depositional morphology, and grain-size distribution of the Longjiayanjiao avalanche were strongly influenced by the uplifted front-edge terrain and the “low-left–high-right” topography in the depositional area. Particle size gradually increased along the movement direction, with large boulders mainly distributed in the central, left, and frontal parts of the deposit, forming an asymmetric depositional structure. The D₅₀ values of deposited rock blocks ranged from 0.16 to 10.28 m, with an overall mean of 0.87 m. (2) The simulation accurately reproduced the movement–deposition process and particle-size distribution characteristics of the avalanche, showing good agreement between simulated and observed depositional ranges. The maximum velocity reached approximately 52 m/s, the average velocity was about 11 m/s, and the maximum block diameter was around 13 m. (3) The avalanche exhibited a dynamic transformation sequence from rock mass to rock blocks to debris. The overall movement and deposition process can be generalized into three stages: chain-type initiation and initial disintegration, collision-induced fragmentation and rapid energy attenuation, and terrain-controlled asymmetric deposition. The results of this study provide an important basis for advancing risk prevention, mitigation, and related research on high-elevation collapses in the Wumeng Mountains.