 Well, when you talk about the hydrogeology of the entire caldera, you probably should be talking or thinking about two domains. A shallow domain that's dominated by the hydrology in the valleys, such as Via Grande, where the water is cold. And then a deeper groundwater system beneath the resurgent dome that is heated by the magma body at depth. And so the geothermal system, which they tried to exploit here about 30 years ago, is the result of heating of shallow groundwater by the magma body to temperatures of about 300 centigrade or 650 Fahrenheit. Up here in the Via's caldera, one of the experiments that was run through the National Labs was the Hot Dry Rock Project, which took advantage of that great heat. They call it Hot Dry Rock because the heat of the rocks drives away the water in the central part of that heating system. But water that comes near the margins of it is heated and then driven by convective forces out through faults and fractures. And it's a continuing process. Water infiltrates every year and feeds into the tail end of the system, and it flows out away from the Hamas Mountains in all directions, along any permeable pathway, which in this case are mainly fault and fracture systems. So the caldera is the source not just for the recharge of the Hamas River surface system, but the recharge for the Via's geothermal system, which takes a much longer path, a much warmer path through the rocks. And the water at the end of that hydrologic system has quite different chemical character from the surface water. The recharge to the geothermal system occurs in these big valleys in the northeast, and the water percolates slowly to depth. I mean, you can imagine that with magma bodies in a resurgent dome, the subsurface is highly fractured, and so water percolates down into those fractures, and eventually it comes in contact with a region of very hot rock caused by convecting heat or conducting heat out of the magma body. And so the water heats up. As it does so, it begins to dissolve solutes out of the rocks, so it becomes somewhat concentrated. It turns into what we call a geothermal brine, and it has a lower density than the surrounding colder waters, and so it kind of rises as a plume to some area, say, 600 meters from the surface, and it boils at that point. And the result of that boiling is that you get fumaroles with gas vents at the boiling point and somewhat lower scattered in different fault zones inside the resurgent dome. And then the water, the subsurface water that has boiled begins to flow to the southwest. It's looking for an easy exit point out of the caldera, and so it flows to the southwest down what we call the Hamas fault zone, which cuts the southwest caldera wall, and those waters flow in the subsurface, and eventually emerge at Soda Dam, Hamas Springs, and so forth. Soda Dam is one of the most spectacular spring deposits in New Mexico. It's certainly the most highly visited place in the state. It's composed of a rock called travertine, which precipitates from water, so it's a freshwater limestone, essentially. Travertine is calcium carbonate that precipitates out of spring waters. Now, you might have hard water in your house, but you won't see nothing like the hard water that comes out of the springs at Soda Dam. That water has a much, much higher dissolved solid load, and it's chock-full of CO2. Those are the bubbles that you see in the spring waters at Soda Dam. And it's a really spectacular thing, but as that water reaches the surface after coming up along a deep fault, it hits the atmosphere and it degasses, just like your fizzing soda pop when you shake it and then open the can. When that CO2 fizzes out of the water, the pH changes drastically, and the calcite drops out and forms a scale over branches and twigs and sticks and everything else in its path. So this carbonate accumulates over long geologic time periods, and that's what Soda Dam itself is, is a buildup of thousands of years, over 5,000 years of calcium carbonate precipitation at that spot in the river.