Still not fully identified at Bugguide, this leaf-cutting bee was bathing in hawkweed (Hieracium sp.) pollen, something it is well-evolved to do. The major pollen-gathering site on Megachile species is under the length of the abdomen and called the ‘scopa‘. The scopa on this bee (not clearly visible) is orange.
You can read more about Megachile species in the garden at The Home Bug Gardener, and for ‘Big-lip’ fanatics, the Canadian Journal of Arthropod Identification has a key to all the known Canadian and Alaskan species at Leafcutter and Mason Bees of the Genus Megachile Latreille (Hymenoptera: Megachilidae) in Canada and Alaska (Cory S. Sheffield, Claudia Ratti, Laurence Packer, Terry Griswold)
Update 10/05/2013: Now identified as Megachile inermis by John S. Ascher at BugGuide. Thank you John!
(Photographed in Edmonton in the North Saskatchewan River valley on 12 August, 2012. Canon T2i with Canon EF 100mm f/2.8 USM Macro and diffused 580 EX II flash. ISO 200, 1/200 sec. @ f13)