PLATES 1. _a_, Butte Ruin. _b_, Aztec Spring Ruin. _c_, Surouaro, Yellow Jacket Spring Ruin. 2. _a_, Blanchard Ruin. _b_, Blanchard Ruin, Mound 2. _c_, Surouaro, Yellow Jacket Spring Ruin. 3. _a_, Acmen Ruin. _b_, Mud Spring Ruin. 4. _a_, Building on rock pinnacle, near Stone Arch, Sand Canyon. _b_, Stone Arch, Sand Canyon. 5. _a_, Tower in Sand Canyon. _b_, Unit type House in Sand Canyon. 6. _a_, Stone Arch House, Sand Canyon. _b_, Cliff-house, showing broken corner. 7. _a_, Scaffold in Sand Canyon. _b_, Storage cist in Mancos Valley. _c_, Pictographs near Unit type House in cave. 8. Double cliff-dwelling, Sand Canyon. 9. _a_, Cliff-dwelling under Horseshoe Ruin. _b_, Cliff-dwelling, Ruin Canyon. 10. _a_, Kiva of cliff ruin, Lost Canyon. _b_, Cliff ruin, Lost Canyon. 11. _a_, Square Tower in Square Tower Canyon. _b_, Tower in McLean Basin. _c_, Ruin in Hill Canyon, Utah. 12. Head of South Fork, Square Tower Canyon. 13. North Fork of Square Tower Canyon, looking west. 14. _a_, Hovenweep House and Hovenweep Castle, from the south. _b_, Hovenweep Castle, from the west. _c_, Hovenweep Castle, from the south. 15. _a_, West end of Twin Tower, showing small cliff-house. _b_, Twin Towers, Square Tower Canyon, from the south. _c_, Tower 4, junction of North and South Forks, Square Tower Canyon. 16. _a_, Hovenweep Castle, with Sleeping Ute Mountain, South Fork, Square Tower Canyon. _b_, Entrance to South Fork, Square Tower Canyon. 17. Stronghold House, Square Tower Canyon. 18. _a_, Head of Holly Canyon. _b_, South side of Hovenweep Castle, Square Tower Canyon. 19. _a_, Holly Canyon group, from the east. _b_, Great House at head of Holly Canyon, from the north. _c_, Unit type Ruin, from the east. 20. _a_, Great House at head of Holly Canyon, from the south. _b_, Ruin B at head of Holly Canyon, from the west. _c_, Great House at head of Holly Canyon. 21. _a_, Great House, Holly Canyon. _b_, Stronghold House and Twin Towers, Square Tower Canyon. 22. _a_, Hovenweep Castle. _b_, Southern part of Cannonball Ruin, McElmo Canyon. 23. _a_, Square tower with rounded corners, Holly Canyon. _b_, Holly Tower in Holly Canyon. _c_, Horseshoe House. 24. _a_, Horseshoe Ruin. _b_, Bowlder Castle, Road (Wickyup) Canyon. 25. _a_, Closed doorway in Bowlder Castle, Road (Wickyup) Canyon. _b_, Broken-down round tower, Square Tower Canyon. 26. _a_, North side of tower, Square Tower Canyon. _b_, D-shaped tower near Davis ranch, Yellow Jacket Canyon. _c_, Model of towers in McLean Basin. 27. Round tower and D-shaped tower in McLean Basin. 28.