I like capris for riding and camping in because they are adaptable from hot to cool temperatures. When it gets really chilly I layer a set of running tights underneath. For less cold days I like long socks with my capris. There are lots of long sock options, but one I sourced locally at MEC.ca was these DeFeet Woolie Boolie socks.
They are wool, they are long and they are black. Thin enough not to be too hot and thick enough to be useful. Layering these with my running tights should be nice and they can be rolled down if it gets hot.
If you are into more snazzy fashion look for colourful ski socks on sale now that winter is over.
They cost $25 & 1yr warranty.