that I've meant to mention and review:

Is "anorthosite". Not the feldspar, but the rock. Product of mafic fractionation. Often rich in ilmenite and apatite. Weathering concentrates these minerals into economic deposits.

It probably makes more sense than anything else.

Oh, I've got some thoughts on these "conglomerates". I'll make it quick, for my own sake.

The Columbia hills are a series of stacked basaltic lava flows.

There were periods of time between flows. (duh)

Water from the lava creates fumerolic activity as lava cools. locallized alteration of vesiculated flow top results.

and/or

Small "sabkhas" develop from seeping ground-water during periods between flow events, creating small, locallized alteration deposits.

When I have more time, I may be able to put together a proper post on this model.