Can You Identify These Weeds?

Weed #1:  These yellow flowers have taken over our property in central Arizona this past month.  The horses were grabbing them up by the mouthful as I walked them past, so I'd like to know what they are called and whether they are poisonous to horses.



Here's a bundle next to one of the tires that the previous homeowners left on the property for us to dispose of, and then next picture is a