Skill level = Advanced.

Optional - Pearl crochet cotton No. 8 (or crochet cotton No. 30), about 380 yards in White and 95 yards each in Yellow, Orange Ombre and Green

For mat measuring about 23-1/2 in. square, use pearl crochet cotton No. 5 and steel hook US size 7

Pattern #1 on page 5 of Magic Crochet.
Pattern 2 in Crochet Monthly.
Pattern uses popcorn and crossed double crochet stitches.