What is this Las Vegas area weed?
Alright, after a lot of searching, I have a proposed ID: Eriogonum deflexum known commonly as skeleton weed or little desert trumpet.  I feel pretty confident of the genus, less so on the species (there are several close candidates).  The family is buckwheat or Polygonaceae.

This plant has basal leaves as yours does, has pretty much leaf-less stems and relatively infrequent flowers, which look quite a bit like your picture.  Reading various descriptions it seems the plant is somewhat variable, it often looks like your pictures but sometimes has more flowers and sometimes the plant is more dense, rounded, shrubby and taller (it probably depends on the moisture and soil quality).  It is a desert species, preferring scrubby areas and washes, widely distributed in Western US deserts.

CalPhotos has a picture which looks to be a good match (credit: Jean Pawek; also, CalPhotos has many other photos).  This photo by Hank Jorgensen looks like a good match too and shows flowers which look similar to yours.

If you see the plant again, bring a picture on your phone and check the flowers carefully. Also the leaves should be hairy/wooly.