A west coast possible itinerary would be Galesburg to Los Angeles to Seattle for one 20,000 point redemption, then Seattle to Sacramento to Galesburg for a second 20,000 point redemption. Since you have the AGR card, you would get 5% of the points back (1,000 points on each redemption).
I used Galesburg so the initial leg would start and the final leg would end at the same station, even though they use different trains. The outbound would be on the Southwest Chief, allowing travel through the Raton Pass. The return trip on my proposed itinerary would be on the California Zephyr.
Note that the outbound could probably stop just about any place between Los Angeles and Seattle, and the return could start from the same station. From Portland (or Seattle, after a layover), you could travel on cash as far east as Wolf Point, MT, and still return to Galesburg on a single AGR redemption.
The trip east of Spokane would not be possible right now because of the line closure due to fire. Also, as Jim mentioned, you would want to book the trip before the new redemption rules go into effect.
(Edited for clarity and to remove a travel option that is not available.)