Originally Posted by
PoliceStateSurvivor
Technically, no.
However, I was told that, given my foreign accent, I could be detained indefinitely if I do not have my passport with me.
That is true anywhere inside the USA - if INS finds a suspected illegal alien they can detain you until your case is reviewed. In practice I would doubt they would detain someone just because they have an accent lack a passport, it woud be more situational specific - in this case probably a car with foreign plates full of undocumented foreigners.
As for the Ag checkpoints, the toll both setup still exists but I haven't seen them occupied in years, they often have signs out saying "closed due to budget cuts". They rarely searched anyone, usually just asked questions to determine if you were bringing in fruits or vegetables.