Regarding the issue of illegal immigration from Mexico to the US, the Sonora Desert could be both a hindrance and an advantage to someone who wants to cross the border into the US illegally. A hindrance due to the heat and difficulty surviving in daytime but at night time where sparsely populated it could allow people to pass unnoticed perhaps. As for rivers, it is conceivable that people could cross the border walking along the bed of a dry stream or small river in the summer when some of the waterways dry up.
