I've been researching and I guess it's palo verde. Agree?

You might want to investigate Arizona Caltrop (Kallstroemia grandiflora), epecially if the plant is an annual herb and not a tree or bush.

Thank you for your input. I appreciate it! It sure looks like it, but the bloom time is wrong. This was pressed in winter and Kallstroemia blooms in summer. But that may be why I pressed it, because I've never seen it before when I do my yearly February Tucson trip. I really have to start taking notes at this point in my life! I have no idea where I got this. Lesson learned.

By the way, I used to be a ranger with the National Park Service and wouldn't pick anything from a museum or park.

You can rule out palo verde. They have tiny yellow orchid-shaped flowers in April, and don't produce leaves (almost microscopic leaves) until summer monsoons.

i've seen Kallstroemia grandiflora bloom only during summer monsoons. It is a low sprawling annual.

Was this in a garden or more natural setting?

Next time you are here, visit both the Tucson Botanical Gardens and also Tohono Chul. Both are good at labeling plants. (You probably already have).

Good luck figuring out what this is. :-)