Possible Clues:

• Sequoia trees
• Crosses houses we'd rebuilt for timber suppliers
• Trees we'd chopped in small areas of land
• Most of those in 23 down and 24 across on top of Sleeping Giants native to America
• Northern California draw
• They're the world's biggest: word does get round
• Towering trees
• World's tallest trees
• Giant conifers
• Tall sequoia trees