Hi Bobbie, I'm a Certified Master Gardener in Oregon and I don't think, judging by your photos or the things you've started about this weed, that it is wild mustard. Wild Mustard grows quite tall, its leaves are more elongated w/ pronounced serration along their edges. From the pictures you've shared your weed looks more prostate, it's leaves are rounded w/ softer serration on is edges. I believe what your weed is is Ranunculus depends aka Creeping Buttercup. It is also invasive, like the Wild Mustard but digging it up and put really won't help. The reason being the little devil can propogate itself from a small section of stem left behind on/in the soil!
Go check out the website weed alert.com, Bobbie. It's a wonderful source of information; the front page has you click on the section of the country you reside in and away you go. This particular weed resides in 42/48 of the
lower 48 states in the USA. Best Wishes and Happy Gardening, Sif👩🏻🌾
