Colors in the clouds

Wow, did you see those clouds at sunset tonight?  Eric and I took a short walk on Salmon Creek Beach after work.  The sky was very dark to the east, and it looked like there could be rain in the hills.  

We had our heads down, watching the wrack line for interesting marine life at our feet.  When we glanced eastward again, there were signs of a faint rainbow forming:

 

 It brightened and lengthened into a very steep arc:

 

At its peak, the rainbow, storm clouds, and angled light on the dunes made for dramatic scenery: 

 

One more closeup of the rainbow and the clouds: