I also live in grassland area in N CA. (lower down, further north, and other side of the valley). As far as I know, mowing or grazing is desirable (and mandated by law!) a certain distance out for fire control. The first 2-3 years I would try to minimize the times I had to do this, and would let the grass grow till the hot dry came on, and then scythe it once, gather this for mulch,
compost, poultry bedding, etc. and then mow the stubble off short. Plenty of seed dropped. Now I'm envisioning adding a sheep or two to the system, so as to convert some of that grass into meat, and spare myself the sweaty hot work of scything and mowing in May or June. The sheep will be in the back, and I'm mowing already in the front and around the gardens, etc.; where the sheep won't be allowed anyway, and making these clippings into bag silage or
hay for summer fodder.
In any case, on just an acre (I have 1 1/2), I would think more than plenty of seed would blow in from outside to keep your
land growing stuff forever, unless you're surrounded by plowed fields. Also, you could deliberately tweak the mix by seeding or selectively mowing. I deliberately avoid patches of clover and wildflowers so as to encourage them, while focusing efforts against thistles, star-thistle, and such like...