I think the earliest mention of Pecans was in The Journey of Alvar Nunez Cabeza de Vaca, published in Anno Domini 1542 (on pages 78 and 79 of my copy). He talks about a particularly poor tribe of Indians who go each year to a place where there are nuts on which they will live for two months: "Even of that they do not always have, since one year there may be some and the next year not."
This is a true account, written by a shipwrecked Spanish sailor who traversed what is now the Southern United States, including Texas and Mexico, living with many different Indian tribes, and survived to return home to Spain and write his story.
It is a book that may change some of your assumptions about a number of things.
You can download it from archive.org or from Google for free, don't even need a special "reader". You could even print it out. My copy is a facsimile (true copy) of the 1905 translation by Fanny Bandelier, published by Rio grande Press in 1964.
He also talks extensively about prickly pears: "tuna", and how important they were to some of the tribes as the mainstay of their diet for much of the year.
I picked up pecans yesterday afternoon, getting up the ones that have fallen before mowing for, what I hope will be, the last time this year. We have a Saint Augustine lawn, so it is easy to see them and I can move about on my knees comfortably. Year before last, I gathered nearly 100 pounds from this one tree. Last year, there was no crop at all to speak of. This year looks promising, I picked up maybe five pounds yesterday. This earliest tree is a Native, and its nuts are small, but they are richer, sweeter, with a much higher oil content than cultivated varieties.
I've mentioned that my trees all drop at different times. It also takes a matter of weeks for all the nuts to fall from a single tree, because I do not flail or shake my trees. If you have ever driven in the South and seen signs that say "No Flailing", now you know what not to do! No hitting trees with sticks from the road!
When I was growing up, lots of people picked up pecans as part of their living, and kids all did it to earn spending money. Southern Oklahoma is Pecan country and they grow wild all over. They remain a major crop for the area.
I take my pecans home to get them cracked, since the machines up there are set for small natives. Here, pecans are also a major crop, but the orchards are mostly cultivated and so the machines are set for cracking larger ones. The machines that crack them have to be set just right so as to crack the shell without breaking the kernal.
Once they've been cracked, they need to be picked out and stored. They will keep for a while at room temperature but will eventually turn rancid. For long term storage, Pecans can be vaccuum packed and frozen, and they will keep indefinitely.