These Araneus females (I'm guessing trifolium based on the guide) are common in our yard in late summer through early fall. They typically make bowers, ranging from fairly simple arches to this beautiful, elaborate one. The bower is about 1 meter off the ground, and it's about 3 cm wide. (I didn't get bugguide hits on "spider bower" or "bower," so I thought this would be a useful set.)

Here's an article on crab spider bowers--which we also see commonly in our yard, on oxeye daisies. (If that's of interest, I can post some photos of them as well.)

And here's a slideshow of several more A. trifolium bowers. (Updated 09 08 10 with a new bower--#8, near bottom of thumbnails--including a shot of the associated web.)