There are a lot of these little little two leaf seedlings of these in my yard which just appeared on my nicely prepared soil.  there They are appearing where the yard has received the best watering; I've been having some challenges finding the best way to water the whole yard.  The yard is probably just under 1000^2 feet and gets full sun during the day.  Right after I planted the buffalo grass - maybe 3 weeks - ago, it seems like everything in Colorado went to seed in my yard.  So maybe it's something else.  That's my concern...that I have to go pull all this stuff.  But if I do, I do.  I just don't want to pull stuff that I want to be there!  I roughed up the ground significantly before laying seed, put a VERY fine layer of compost down (which I've used before), and covered it with about 1/4-1/2" of topsoil following the recommendations of theCSU extension office.  We've had a lot of slow rain (for CO) the last few weeks and I've been watering fairly consistently.  I set a regular digital thermometer on the ground for about an hour a couple days ago as I was curious about ground temps.  It registered 63.  We have had a snow since I planted and one night below freezing but our temps have been high (70-85) some days for this time of the year.  

Thanks!

(I submitted this Q a few minutes ago but it doesn't look like it posted.)