Watercolor is such a versatile medium. You can paint your watercolors on so many different surfaces from paper to boards to even Yupo, a synthetic surface. Gouache can be used with your watercolors if you need to achieve an opaque quality. This versatility makes it useful to record an experience or a setting right on the spot. And of course, you can paint from memory, too.
This watercolor was painted on one of the inside covers of a watercolor block I have been using. This smooth surface has nearly a cardboard thickness too it.
I enjoy experimenting with any surface I can find to see how the pigment responds to the paper. For example with hot press paper the pigment sits on the surface while with cold press or rough paper you can utilize a dry brush technique which can suggests texture such as on rocks or grasses along the shore.