You have discovered annual bluegrass! Crabgrass is a warm season plant that germinates in April and grows into the summer and dies with the first frost. We do not have bad crabgrass problems in western Oregon.
Annual bluegrass (Poa annua) is one of the two grasses that dominates lawns in western Oregon and Washington. The other is bentgrass. The only way a homeowner can kill annual bluegrass is by selectively spraying out the patches with glyphosate (e.g. Roundup), and then reseeding. Be careful as glyphosate will kill any plant it touches.
To give you an idea how difficult it is to control annual bluegrass, all golf courses in western Oregon and Washington older than 25 years have converted to nearly 100% annual bluegrass in spite of many having million dollar or more maintenance budgets and spending a lot of money to try and control it. They have all failed.
My recommendation is to embrace it. In a few years, the patches will coalesce and you won't have the mosaic effect. You can still have a very nice lawn. Go look at a local golf course and see how nice it looks. The key is good maintenance: consistent mowing, fertilization, and irrigation. Annual bluegrass does not like drought, so it is important to irrigate it frequently in the summer.