| 1902 Productions INC DBA Ab Construction | Andrew Craig Brown | — | (530) 598 5175 | GC, remodel, ADU | Etna · Siskiyou County | — | — |
| 2 B Fencing | 2 B Fencing | — | (916) 261 2181 | Other | Mc Cloud · Siskiyou County | — | — |
| 4th Gen Flooring | 4th Gen Flooring | — | (530) 598 5817 | Other | Yreka · Siskiyou County | — | — |
| 6 Point Construction | Richard Allen Evans | — | (530) 643 0891 | GC, remodel, ADU | Yreka · Siskiyou County | — | — |
| A & M Well Drilling INC | Dianne Theresa Jar Tweedy | — | (530) 905 0695 | Other | Hornbrook · Siskiyou County | — | — |
| A 2 D Painting | A 2 D Painting | — | (949) 395 5412 | Windows, patio, painters | Weed · Siskiyou County | — | — |
| A Allison Painting | A Allison Painting | — | (530) 840 0110 | Windows, patio, painters | Mt Shasta · Siskiyou County | — | — |
| A Cut Above Tree Service INC | Nicholas Lee Borgatti | — | (530) 643 2155 | Tree | Mt Shasta · Siskiyou County | — | — |
| A D O'bannon Builder | A D O'bannon Builder | adobuilder@gmail.com | (707) 322 2372 | GC, remodel, ADU | Mt Shasta · Siskiyou County | — | — |
| A-1 Drains | A-1 Drains | — | (530) 598 2789 | Other | Etna · Siskiyou County | — | — |
| Able Tree Services | Giselle Demarious Nova | — | (530) 859 0384 | Tree | Mt Shasta · Siskiyou County | — | — |
| Advanced Roofing Techniques | Duane Otis Orsburn | advancedroofingtech@yahoo.com | (530) 475 3056 | Other roofers | Hornbrook · Siskiyou County | — | — |
| Advantage Paving & Excavating INC | Clayton William Hansen | — | (530) 598 7759 | Other | Yreka · Siskiyou County | — | — |
| Air Construction & Excavation | Darren Paul Rose | — | (530) 842 2224 | Other | Yreka · Siskiyou County | — | — |
| Alan's Complete Landscaping Service | Alan Charles Taylor | — | (530) 925 9180 | Windows, patio, painters | Dunsmuir · Siskiyou County | — | — |
| Aldrich Painting | Aldrich Painting | — | (530) 598 6343 | Windows, patio, painters | Yreka · Siskiyou County | — | — |
| All In One Enterprise | All In One Enterprise | interested@domainmarket.com | (530) 468 2529 | Windows, patio, painters | Fort Jones · Siskiyou County | — | — |
| All Trade Mechanical And Electric | Jacob Lee Pritchard | office@alltradeservices.com | (530) 918 5547 | HVAC | Mount Shasta · Siskiyou County | — | — |
| Allen B Headley | Allen B Headley | — | (951) 751 1339 | GC, remodel, ADU | Weed · Siskiyou County | — | — |
| Alpine C S W Construction | Kenneth Alan Roseberry | — | (530) 863 0520 | GC, remodel, ADU | Mt Shasta · Siskiyou County | — | — |
| Alpine Engineering | Alpine Engineering | — | (530) 514 1758 | Other | Mc Cloud · Siskiyou County | — | — |
| Altes Engineering INC | Ruth Renee Altes | — | (530) 925 1775 | Other | Mt Shasta · Siskiyou County | — | — |
| Amaral Electric | Zachary Daniel Amaral | — | (530) 262 1594 | Electricians | Weed · Siskiyou County | — | — |
| America Reforesting | Martinez Adolfo Rivera | — | (541) 840 2410 | Tree | Yreka · Siskiyou County | — | — |
| American River Irrigation | American River Irrigation | — | (916) 206 0122 | Windows, patio, painters | Dunsmuir · Siskiyou County | — | — |
| Amped Electric | Carlos Alberto Jr Barros | — | (530) 202 0932 | Electricians | Fort Jones · Siskiyou County | — | — |
| Ap Earthworks | Ap Earthworks | — | (530) 514 0908 | Other | Mt Shasta · Siskiyou County | — | — |
| Apar Custom Building | Apar Custom Building | — | (310) 529 1826 | GC, remodel, ADU | Dunsmuir · Siskiyou County | — | — |
| Apex Electrical Systems | Austin Michael Morrissey | — | (562) 637 3975 | Electricians | Mc Cloud · Siskiyou County | — | — |
| Apex Roofing California | Apex Roofing California | — | (530) 842-0098 | Other roofers | Yreka · Siskiyou County | — | — |
| Apollo Electric Co | Michael Shane Hlynsky | chrischatzis@gmail.com | (801) 554-3344 | Electricians | Mount Shasta · Siskiyou County | — | — |
| Archer Mechanical | Archer Mechanical | — | (530) 925 5748 | HVAC | Mount Shasta · Siskiyou County | — | — |
| Arnold Krooms & Black Butte Forge | Arnold Jerome Krooms | — | (530) 261 1913 | Other | Mt Shasta · Siskiyou County | — | — |
| Ascent Forestry | Ascent Forestry | info@indiantypefoundry.com | (209) 336 3031 | Tree | Mount Shasta · Siskiyou County | — | — |
| Atwood Restoration & Construction | Atwood Restoration & Construction | — | (530) 842-7771 | Restoration | Yreka · Siskiyou County | — | — |
| Awm Construction INC | Adam Wesley Mc Williams | awmconstruction@msn.com | (530) 938 9677 | GC, remodel, ADU | Weed · Siskiyou County | — | — |
| B & A Sealcoating | B & A Sealcoating | — | (530) 643 6138 | Other | Yreka · Siskiyou County | — | — |
| B K Construction | Brian Kenneth Kische | — | (530) 842 5221 | GC, remodel, ADU | Yreka · Siskiyou County | — | — |
| B M Construction & Frame Work | Breton Albion Mc Intyre | — | (530) 859 3773 | GC, remodel, ADU | Weed · Siskiyou County | — | — |
| B N G Finish Products INC | Brian Douglas Eastlick | — | (530) 925 9767 | GC, remodel, ADU | Etna · Siskiyou County | — | — |