Diagonal 'Granny Square' Baby Blanket

Design: A bias-stitched, or diagonal, large granny square, crocheted in two triangles from the corners up. (The picture is of one-quarter of the blanket, which is folded...I will update with better pictures once I can get them.)

Materials: Approximately 600 yds. of sport-weight yarn for main body of blanket; a smaller amount of yarn (maybe 50 yds.) for center seam and trim.  This example used two skeins of Bernat Softee Baby (Sport DK) in Flannel, with navy blue sport weight stash yarn. (The exact yarn is and will remain a mystery.)  Size H crochet hook.

Pattern: Row 1: Ch 4, dc x 3 in 4^th chain from hook, ch 3, turn

Row 2: 3 dc in 1^st dc, ch 1, 3 dc in 3^rd dc, tr in turning chain, ch 3, turn (2 shells)

Row 3: 3 dc in 1^st dc, ch 1, 3 dc in 3^rd dc, ch1, tr in turning chain, ch 3, turn (2 shells)

Row 4: 3 dc in 1^st dc, ch 1, 3 dc in 1^st ch-1 space, ch 1, 3 dc in last dc, ch 1, tr in turning chain, ch 3, turn

Row 5: 3 dc in 1^st dc, ch 1, 3 dc in 1^st ch-1 space, and in each ch-1 space across, ch 1, 3 dc in last dc, ch 1, tr in turning chain, ch 3, turn

Repeat row 5 until triangle is desired size (will be adding one 3-dc shell per row)

Make 2 triangles and attach across diagonal to make a square.

I needed 42 rows for each triangle to make a 30 x 30 blanket (after adding the border). 

To attach the two triangles, I used a single crochet join that makes a raised edge on one side (the 'right side'):

and a flat seam on the other:

I had to experiment a bit before I got the seam right.  Holding the right sides of the work together, I worked in only the two inner loops that were touching, like this:

Here is another view from the top showing that the single crochet is worked into the inner loops:

It also took me a while to pick a border stitch I liked -- almost as long as it took me to make the squares!  After many attempts at picots and a prolonged battle with the reverse single crochet stitch, I settled on one row of single crochet and one row of slip stitch to finish the edge:

This is the first pattern I have written so please let me know of errors or elements that are not clear...