Is it normal to haul a big anvil into the woods just for a forge session?

The side-angle pipe is your main problem. With a ground forge you want the air coming up from underneath the coal, otherwise you're just blowing across the top of the pile and only the part of the bar sitting right in the blast gets hot. When I ran a dirt forge I dug a little chamber maybe eight inches deep, laid a grate of steel bar or even some old grate iron across it, packed coal on top, and ran the pipe into the side of the cavity below the grate. That way the air has to travel up thru the whole coal bed before it escapes, and the fire burns hottest right where the air exits. Side-in from above the coal basially gives you a campfire with a fan on it. The damp ground absolutely was stealing heat too. Wet soil pulls heat out of the fire and steams, which cools things down and makes your coal work harder. Laying fire brick down isn't overkill at all, it's the cheap fix. Even a half dozen bricks in a flat spot under the fire makes a noticable difference. Some people line the whole depression with brick or flat stones and skip the deep pit entirely, just building the fire on top with the pipe coming in low from the side, under the coal edge. That works pretty well too and drains better if the ground is soaked. A couple other things that helped mine. Get a deeper coal bed, like three or four inches at least, and coke it up before you stick the bar in. Green coal right on the steel gives slow, dirty heats. And aim the hair dryer more at building a concentrated pocket of glowing coke than at the bar itself. Ball the fire up tight around the work instead of spreading it out flat.

Also, if you're hauling that anvil a quarter mile regularly, a two-wheel hand cart and a ratchet strap will save your back. Learned that one the hard way.

Yeah the grate trick made all the difference for me too. I used an old cast iron stove grate I found at a yard sale over a dug pit and my heats went from barely orange to working hot in a couple minutes. One thing I'd add is bring a bucket, damp ground got so bad at my spot that I ended up digging a little trench around the fire area to keep runoff water out. Kept the bricks underneath dry and the whole thing stayed hotter way longer.

Cool thread. I've never done a ground forge but I do a lot of camp cooking over coals and the wet ground thing tracks with what I've seen. A fire on soaked soil just never burns right, everything steams. I started hauling a couple of concrete pavers out to my fire pit spot and the difference was instant. Cheaper than fire brick too if you've got leftovers from a patio project sitting around. Question for the OP, how did you even carry your anvil that far? I struggle getting my gear to a campsite half that distance and mine weighs nothing compared to 110lb.

Update: I switched the air direction to flow up from underneath the coal, using a makeshift chamber that worked much better. I also laid down some concrete pavers around the spot, which made a huge difference in retaining the heat. Heating the anvil is much quicker now.