Another obstacle is the variety of flora. There are sometimes-dense riparian vegetation, open grassy areas, trees and brush in canyons, pinon-juniper regions, desert shrub, mountain shrub, and montane life communities. Some are easy to walk through, others need more or less bushwhacking. That's hard to read from the map.
This page has modest objectives. Very simply: from the jumping-off point of the Echo Park campground, this page describes an upstream trail and a downstream trail. Each is unmarked on my maps, unmaintained, but in good shape. This page will confirm to you, Gentle Reader, that you can get from point X to points Y and Z.
Our trip was in mid-May 2011, a time of very high water. At times of low water, some of Scott's photos from the park suggest that walking on sandy beaches is often a possibility. I would guess that's true for the Sand Creek connector here but not for the Mitten Park trail, but that's just a guess.
Well before that point, turn right, down the Echo Park Road. The switchbacks through red sandstone would clearly be impassible gumbo when wet. Lower down, the single-lane dirt road has ruts, occasional rocks, and (improved) stream crossings that make it inappropriate for low-clearance vehicles. We did not need four-wheel drive, but I can imagine times when you would.
About nine miles in, a spur road goes down to Echo Park. Be sure to stop at the rock art and at Whispering Cave, and check out the Chew Ranch if you like. There is an official campground in Echo Park with picnic tables and two outhouses, but no water.
Mitten Park Trail
There's some minor route-finding along the ledges at the highest point of the trail. You can probably go high if you're a bighorn sheep, or go low if you want the exposure above the river. Generally speaking, humans will do best to stick to the middle options through this stretch.
In two places you have to go up/down a "face" about 4 feet high. This poses no problem for adults but kids will need help "scrambling."
From the rocky ledges, descend to the grassy area of Mitten Park. Even at high water there was a lunchspot-worthy sandbar along the river. There seems to be some light bushwhacking options ahead, and perhaps some scree-climbing options up toward Harper's Corner, but we didn't pursue either of those.
Length of the trail is about 1.5 miles each way.
Sand Canyon Connector Trail
From the campground, go upriver past the raft put-in to a circle in sight of the ranger cabin. Find a place to park.
Walk across the grass, staying close to the river when you have options. There are some tempting forks in the trail to the right but they dead end. At the confluence of the Green and Yampa, go up and over a small bluff on your right. You may or may not see a post or two. If you see them, follow them; otherwise beeline across the field.
The slopes below the cliffs gradually squeeze out the flat land here. Close to the river you'll see a trail clearly. As you progress up the Yampa, you'll see about 3-5 game trails criss-crossing the hillside. Generally speaking, you should try to stay high when given options.
In one 20-foot section the soil has slipped down the hillside, leaving a narrow trail on top. It's still eroding, and at some point a hiker will have a long slide into home plate at the bottom of the hill.
The trail descends to the mouth of Sand Canyon on the Yampa, and to a dense stand of cottonwoods on the beach. There's an official, but unmaintained trail up Sand Canyon to the Yampa Bench Road.
Length of the connector trail is about 2 miles each way. The length of Sand Canyon (which we didn't do) is another 2.5 miles.