Where your water goes

Rain that falls on Brownsville ends up in the Gulf of Mexico

1. Your sub-basin

   Lower Rio Grande

2. then

   Rio Grande

3. It arrives here

   Gulf of Mexico

This water joins the largest drainage in North America and travels south for thousands of kilometres to the Gulf. What runs off the fields upstream of you arrives there too, which is why a dead zone the size of a small country forms off Louisiana each summer.

Basin 130900 (USGS hydrologic unit)

Under your feet

Brownsville sits on river deposits

About 11,700 years old — from the ice ages and since — the most recent chapter.

All the kinds of rock, and how each one forms →

1. At the surface11,700 years oldNeither way

   River deposits

   Silty and sandy flood-plain alluvium · Holocene

   What it is

   Alluvium: loose sediment laid down by moving water on a floodplain, a delta or a bar. Some of it is decades old rather than millions of years.

   How it wears

   It is already weathered; that is what it is. The river sorts it, moves it, and puts it down somewhere else.

   What it means above ground

   The deepest, most fertile and most level soil in any landscape, which is why floodplains are farmed and towns get built on them. Also the ground that floods, and the ground that liquefies in an earthquake.

2. Below, layer 211,700 years oldNeither way

   River deposits

   Alluvium in Rio Grande, subdivided into areas predominantly of sand · Holocene

   What it is

   Alluvium: loose sediment laid down by moving water on a floodplain, a delta or a bar. Some of it is decades old rather than millions of years.