The article I posted about Zebulon Pike and Governor Alencastre (correct spelling, from other sources) caused me to check other sources in my library, esp. Major Z. M. Pike, 1810, "An Account of Expeditions to the Sources of the Mississippi, etc. etc. and a Tour through the Interior Parts of New Spain.... 1807," Binns, March of America Facsimile ser. 57; and R. E. Twitchell, 1911, "Leading Facts of New Mexico History," vol. one.

The story by Marc Simmons has errors, and parts are questionable.

Pike (mostly from his book) and his party were approached by the Spanish troops at his 'Fort' which Pike thought was near the headwaters of the Red River. The Spaniards told him it was near the headwaters of the Rio Grande del Norte, and that the Red River was some eight days hard march from Santa Fe; an escort there was offered, but his excellency (Alencastre) was anxious to see him in Santa Fe.
The escorted trip, though carried out with all courtesy, of course was mandatory. During his stay in Santa Fe, and later on the escorted journey to Chihuahua, his captive party was provided with food, clothing and animals for transport. Pike was questioned, but politely; the Spanish deprived him of his maps. Pike himself and some others were entertained at the homes of leading citizens, and Pike mentions the fine wines and gracious hospitality received in Alburquerque (original spelling).

As to the 'fort' described in Simmon's article, its origin and use is questionable.
1. It resembles a pueblo structure, esp. the clustered rooms; the round towers on the walls occur on some early pueblo-Anasazi settlements; at least one such tower is preserved at a still-active pueblo.
2. There is no mention in Spanish archives of such a structure; if Twitchell and subsequent historians had found any information, they would have noted the fact.
It seems likely that the 'fort' was an abandoned pueblo, but since it now is under water, proof is lacking. I do not have information on archaeological work in the area, but field studies may have been done there.