I spent some time checking out the USGS Seamless Data Distribution system tonight and plotting all sorts of elevation maps. You can include hydrologic data, roads, aquifer info and more stuff, but the coolest thing was plotting a topo profile between selected points. Click “read more” for a profile across the island where I live generated by the site.
For folks unfamiliar with this kind of GIS (Geographical Information System) data, this USGS site functions like Microsoft’s Terraserver except that it is designed to display spacial (in this case, elevation) data as opposed to satellite pictures. Since you can easily turn layers for roads and bodies of water on and off, leaving only the shaded topographical info, you can see the hills and valleys clearly and really get a good feeling for the “lay of the land”. Although it’s hard to see in the small capture I have here, Carman’s River passes through a “cut” in the southern moraine which professors at Stony Brook think was made by a huge volume of water that was once held in a lake behind that moraine. If you’re familiar with the Carman’s River, it’s hard to imagine that stream (river in this case is a misnomer!) eroding the wide swath south of the cut. The wide “flood plain” is clearly evident in the topo on the USGS site. The prominent hill in the center of the topo image is Bald Hill which is a “kame”, a hill of rock dumped as water ran through or under a glacier. It is thought to mark the very edge of the glacier before it retreated. A neat utility on the USGS page allowed me to confirm the height at 297ft at the hill’s summit (the profile doesn’t pass through Bald Hill).

Making a cross-sectional profile across Long Island was fun. I picked a line from Port Jefferson harbor on the Long Island Sound over the two moraines through the Smith Point penninsula and over fire island to the Atlantic Ocean. The line trends North-west / South-east. Port Jeff is on the left side of the graph and you can see the tiny bump of fire island on the far right. Point 2 is a little bit North of my town. Obviously? the vertical scale is exaggerated in this plot since the island is about 22 miles wide along this line.