[4] In 2009, H. oregonensis was included on a list of animals petitioning for the endangered species label, but there was not enough scientific information available for it to be considered as such, so it remains unevaluated to the present day.

[2] The carapace in the hind region is free from transverse ridges, but contains three teeth between the orbit and lateral angle.

[2] The entire genus is restricted to the Pacific Ocean, except for Hemigrapsus affinis which lives along the Atlantic coasts of South America, from Cape San Roque (Rio Grande do Norte state, Brazil) to the Gulf of San Matías (Patagonia, Argentina), and population of Hemigrapsus sanguineus which have been introduced from the species' native range in East Asia to the Atlantic coast of the United States from Portland, Maine to North Carolina, and to the English Channel and North Sea.

[8] This species typically lives under rocks in intertidal zones, but can also be found along shorelines, and in mud flats, algal mats, eelgrass beds and the tidal mouths of large rivers (estuaries).

Its geographical range in the United States spans from Resurrection Bay to Bahía de Todos Santos.

[4] Hemigrapsus oregonensis's diet primarily consists of diatoms and green algae, but it will occasionally eat meat, if accessible.

[9] The chief difference between H. estellinensis and other species in the genus is the extensive pattern of rust-red spots on the animal's "drab green" carapace.

[11] The springs originally produced water with a salinity of 43‰ that fed the Prairie Dog Town Fork of the Red River.

[9] The United States Army Corps of Engineers built a dike around the Estelline Salt Springs in January 1964,[13] which has reduced the chloride load on the Red River by 220 tonnes (240 short tons) per day.

[13] As early as December 1962, attempts to find further living individuals of H. estellinensis were unsuccessful, and it was probably extinct before Creel's description was published in 1964.

It is a good digger and prefers to stay hidden in burrows it has dug during the day, only coming out to feed at night.

[6] H. oregonensis may also house a parasitic isopod known as Portunion conformis in its perivisceral cavity, but this is not apparent through observation with the naked eye.

However, P. crassipes can be distinguished by the transverse ridges located on its carapce, and its two teeth between the orbit and lateral angle, as opposed to H. oregonensis's three.