| Business | Phone |
| Bryan A Stirrat & Assoc 1360 Valley Vista Dr, Diamond Bar 91765 | (909) 860-7777 |
| Loren C Phillips & Assoc 22632 Golden Springs Dr # 350, Diamond Bar 91765 | (909) 396-9636 |
| Pfeiler & Assoc Engineers 660 N Diamond Bar Blvd # 100, Diamond Bar 91765 | (909) 860-5850 |
| Civil Trans Inc 732 N Diamond Bar Blvd, Diamond Bar 91765 | (909) 396-1131 |
| Lin Consulting Inc 21660 Copley Dr # 270, Diamond Bar 91765 | (909) 598-0899 |