Unmanned Aerial Vehicle (UAV) can enhance communication quality in wireless systems. It is helpful to address the blockage problem in mountainous regions. However, it has high energy consumption. In this paper, we propose a novel blockage model converted blockage region constraints into linear constraint. Then, the joint resource allocation and trajectory design scheme is proposed to maximize energy efficiency (EE). Specifically, we model the blockage effect caused by mountains. The Dinkelbach algorithm is designed to address the fractional objective function for EE. Then, we develop an iterative block coordinate descent (I-BCD) algorithm that alternately optimizes resource allocation and trajectory design subproblems. The resource allocation subproblem employs a dual-loop structure with Lagrangian duality to obtain closed-form solutions for power and bandwidth allocation. Meanwhile, the trajectory optimization uses successive convex approximation (SCA) to transform non-convex constraints into convex optimization problems. Simulation results demonstrate that the proposed scheme improves the EE compared with the benchmark schemes for UAV-assisted communications in mountainous regions.