1915 Panama-Pacific Exposition
(read how to identify your stamp below)
You have a stamp that commemorated the Panama-Pacific Exposition held in San Francisco in 1915. The lower values are quite common, particularly the 2¢. The orange 10¢ is less common. Using the illustration below first identify which perforation your stamp has. Then using the two sets of images below click on the stamp which closely matches yours, this will take you to the page with more details.