Abonner for at downloade
HL-1 Styled Rocks and Cliffside

This addon will applying a recolor to rocks and cliffside similar of Half-Life 1.

If this not work. You may vpk files put to the custom folder.

1. Step Find the addon:

Steam\steamapps\workshop\content\362890\2641504530

bm_classic_rocks_000
bm_classic_rocks_001
bm_classic_rocks_002
bm_classic_rocks_003
bm_classic_rocks_004
bm_classic_rocks_005
bm_classic_rocks_006
bm_classic_rocks_007
bm_classic_rocks_008
bm_classic_rocks_009
bm_classic_rocks_010
bm_classic_rocks_011
bm_classic_rocks_dir

and put to the

common\Black Mesa\bms\custom

If you don't see Custom Folder. There's tutorial
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=502670746