A blind valley or California Valley as it's sometimes called is ideal for situations where a new roof must tie into an existing roof. It can also be used for other things such as decorative false gables or even chimney crickets. In this type of valley the main roof is framed and sheathed as usual and the intersection of the addition roof is framed on top of the main roof. This is the most flexible valley option that Easy Rafters provides in that it can be used for intersecting roofs with unequal slopes and/or spans.
note: if the slope of the addition roof is shallow and the seat cut of the jack rafters is long, you may need to use very wide valley plates or insert filler strips to ensure that the jack rafters are sufficiently supported along their seat cuts.