Step 1--The Columns
The wooden structure rests on stone-veneer columns that are 18 inches square and 3 feet high. We decided to go with stone because the front door of my house is surrounded by stone. Using the same material visually unifies the house and arbor.
To make the stone-veneer columns, we first excavated a 1-foot-deep footing for each column. In each footing, we placed cinder blocks, drove iron rebar through the holes into the ground, and then mortared the blocks in place. We mortared together additional cinder blocks atop the bottom ones until we reached the height we wanted and filled the holes in the blocks with concrete.
Next, we inserted a steel U-bracket into the fresh concrete at the top of each column. This type of bracket consists of a galvanized box attached to an 18-inch metal rod that goes down the center of the column. We propped up each bracket so that when the concrete dried, the bottom of the box would be about an inch above the topmost cinder blocks. You'll see why in just a minute.
Step 2--About Face
Next, we hid the cinder blocks behind a veneer of cut native stone. We selected stones that were basically flat, smooth, and about the same size so they would stack easily and give a neat, crafted look. We secured the stones by cementing them on the inside edge, next to the cinder blocks, hiding the cement to give the appearance of dry-stacked columns.
As a final touch, we slid 1-inch-thick "capstones" under the galvanized box atop each column and mortared them to the stones below. Then we used silicone caulk to seal the edges around the bottom of the box to prevent water from entering the columns from above.