from the CRC website (linked to in earlier post):
This last caveat poses a particular concern for amaranth and quinoa, as these small seeds are often packaged on the same equipment as other small grains such as wheat, barley and oats, which means that they can only be used after being carefully checked that no chametz grains are mixed in. In practice, most consumers are not familiar enough with the difference between one grain and the next to be able to perform this check, and as a result they cannot use them for Pesach.
This year, we were once again able to confirm that the whole grain quinoa sold under the Ancient Harvest and Trader Joe brand names, and bearing the KOAOA/Half- Moon K kosher certification, are produced in plants which do not package chametz grains, and are therefore suitable for Pesach use. [This does not apply to the quinoa flour or flakes]. It is worth verifying this information before each Pesach to make sure the information remains accurate.