My first question would be are you sure you have crabgrass? It's common in this area for folks to say crabgrass when they actually are dealing with bermudagrass, which is much more difficult to manage. Your question about needing to get rid of the remaining roots indicates that it may be bermudagrass. You can send me some pictures and we can probably identify it from them, or even better would be to bring a sample to the Master Gardener plant clinic at 569 Hanley Rd, Central Point. They're open Monday through Friday, 10 AM - 2 PM.
Or you can identify it yourself and learn about management from these publications, both produced by the University of California Integrated Pest Management program.
Crabgrass Management - http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7456.html
Bermudagrass management - http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7453.html